Theory Dirichlet_Series_Analysis
section ‹Analytic properties of Dirichlet series›
theory Dirichlet_Series_Analysis
imports
"HOL-Complex_Analysis.Complex_Analysis"
"HOL-Library.Going_To_Filter"
"HOL-Real_Asymp.Real_Asymp"
Dirichlet_Series
Moebius_Mu
Partial_Summation
Euler_Products
begin
text ‹Conflicting notation from \<^theory>‹HOL-Analysis.Infinite_Sum››
no_notation Infinite_Sum.abs_summable_on (infixr "abs'_summable'_on" 46)
text ‹
The following illustrates a concept we will need later on: A property holds for
‹f› going to ‹F› if we can find e.\,g.\ a sequence that tends to ‹F› and whose elements
eventually satisfy ‹P›.
›
lemma frequently_going_toI:
assumes "filterlim (λn. f (g n)) F G"
assumes "eventually (λn. P (g n)) G"
assumes "eventually (λn. g n ∈ A) G"
assumes "G ≠ bot"
shows "frequently P (f going_to F within A)"
unfolding frequently_def
proof
assume "eventually (λx. ¬P x) (f going_to F within A)"
hence "eventually (λx. ¬P x) (inf (filtercomap f F) (principal A))"
by (simp add: going_to_within_def)
moreover have "filterlim (λn. g n) (inf (filtercomap f F) (principal A)) G"
using assms unfolding filterlim_inf filterlim_principal
by (auto simp add: filterlim_iff_le_filtercomap filtercomap_filtercomap)
ultimately have "eventually (λn. ¬P (g n)) G"
by (rule eventually_compose_filterlim)
with assms(2) have "eventually (λ_. False) G" by eventually_elim auto
with assms(4) show False by simp
qed
lemma frequently_filtercomapI:
assumes "filterlim (λn. f (g n)) F G"
assumes "eventually (λn. P (g n)) G"
assumes "G ≠ bot"
shows "frequently P (filtercomap f F)"
using frequently_going_toI[of f g F G P UNIV] assms by (simp add: going_to_def)
lemma frequently_going_to_at_topE:
fixes f :: "'a ⇒ real"
assumes "frequently P (f going_to at_top)"
obtains g where "⋀n. P (g n)" and "filterlim (λn. f (g n)) at_top sequentially"
proof -
from assms have "∀k. ∃x. f x ≥ real k ∧ P x"
by (auto simp: frequently_def eventually_going_to_at_top_linorder)
hence "∃g. ∀k. f (g k) ≥ real k ∧ P (g k)"
by metis
then obtain g where g: "⋀k. f (g k) ≥ real k" "⋀k. P (g k)"
by blast
have "filterlim (λn. f (g n)) at_top sequentially"
by (rule filterlim_at_top_mono[OF filterlim_real_sequentially]) (use g in auto)
from g(2) and this show ?thesis using that[of g] by blast
qed
text ‹
Apostol often uses statements like `$P(s_k)$ for all $k$ in an infinite sequence
$s_k$ such that $\mathfrak{R}(s_k)\longrightarrow\infty$ as $k\to\infty$'.
Instead, we write @{prop "frequently P (Re going_to at_top)"}. This lemma shows that
our statement is equivalent to his.
›
lemma frequently_going_to_at_top_iff:
"frequently P (f going_to (at_top :: real filter)) ⟷
(∃g. ∀n. P (g n) ∧ filterlim (λn. f (g n)) at_top sequentially)"
by (auto intro: frequently_going_toI elim!: frequently_going_to_at_topE)
lemma surj_bullet_1: "surj (λs::'a::{real_normed_algebra_1, real_inner}. s ∙ 1)"
proof (rule surjI)
fix x :: real show "(x *⇩R 1) ∙ (1 :: 'a) = x"
by (simp add: dot_square_norm)
qed
lemma bullet_1_going_to_at_top_neq_bot [simp]:
"((λs::'a::{real_normed_algebra_1, real_inner}. s ∙ 1) going_to at_top) ≠ bot"
unfolding going_to_def by (rule filtercomap_neq_bot_surj[OF _ surj_bullet_1]) auto
lemma fds_abs_converges_altdef:
"fds_abs_converges f s ⟷ (λn. fds_nth f n / nat_power n s) abs_summable_on {1..}"
by (auto simp add: fds_abs_converges_def abs_summable_on_nat_iff
intro!: summable_cong eventually_mono[OF eventually_gt_at_top[of 0]])
lemma fds_abs_converges_altdef':
"fds_abs_converges f s ⟷ (λn. fds_nth f n / nat_power n s) abs_summable_on UNIV"
by (subst fds_abs_converges_altdef, rule abs_summable_on_cong_neutral) (auto simp: Suc_le_eq)
lemma eval_fds_altdef:
assumes "fds_abs_converges f s"
shows "eval_fds f s = (∑⇩an. fds_nth f n / nat_power n s)"
proof -
have "fds_abs_converges f s ⟷ (λn. fds_nth f n / nat_power n s) abs_summable_on UNIV"
unfolding fds_abs_converges_altdef
by (intro abs_summable_on_cong_neutral) (auto simp: Suc_le_eq)
with assms show ?thesis unfolding eval_fds_def fds_abs_converges_altdef
by (intro infsetsum_nat' [symmetric]) simp_all
qed
lemma multiplicative_function_divide_nat_power:
fixes f :: "nat ⇒ 'a :: {nat_power, field}"
assumes "multiplicative_function f"
shows "multiplicative_function (λn. f n / nat_power n s)"
proof
interpret f: multiplicative_function f by fact
show "f 0 / nat_power 0 s = 0" "f 1 / nat_power 1 s = 1"
by simp_all
fix a b :: nat assume "a > 1" "b > 1" "coprime a b"
thus "f (a * b) / nat_power (a * b) s = f a / nat_power a s * (f b / nat_power b s)"
by (simp_all add: f.mult_coprime nat_power_mult_distrib)
qed
lemma completely_multiplicative_function_divide_nat_power:
fixes f :: "nat ⇒ 'a :: {nat_power, field}"
assumes "completely_multiplicative_function f"
shows "completely_multiplicative_function (λn. f n / nat_power n s)"
proof
interpret f: completely_multiplicative_function f by fact
show "f 0 / nat_power 0 s = 0" "f (Suc 0) / nat_power (Suc 0) s = 1"
by simp_all
fix a b :: nat assume "a > 1" "b > 1"
thus "f (a * b) / nat_power (a * b) s = f a / nat_power a s * (f b / nat_power b s)"
by (simp_all add: f.mult nat_power_mult_distrib)
qed
subsection ‹Convergence and absolute convergence›
class nat_power_normed_field = nat_power_field + real_normed_field + real_inner + real_algebra_1 +
fixes real_power :: "real ⇒ 'a ⇒ 'a"
assumes real_power_nat_power: "n > 0 ⟹ real_power (real n) c = nat_power n c"
assumes real_power_1_right_aux: "d > 0 ⟹ real_power d 1 = d *⇩R 1"
assumes real_power_add: "d > 0 ⟹ real_power d (a + b) = real_power d a * real_power d b"
assumes real_power_nonzero [simp]: "d > 0 ⟹ real_power d a ≠ 0"
assumes norm_real_power: "x > 0 ⟹ norm (real_power x c) = x powr (c ∙ 1)"
assumes nat_power_of_real_aux: "nat_power n (x *⇩R 1) = ((real n powr x) *⇩R 1)"
assumes has_field_derivative_nat_power_aux:
"⋀x::'a. n > 0 ⟹ LIM y inf_class.inf
(Inf (principal ` {S. open S ∧ x ∈ S})) (principal (UNIV - {x})).
(nat_power n y - nat_power n x - ln (real n) *⇩R nat_power n x * (y - x)) /⇩R
norm (y - x) :> Inf (principal ` {S. open S ∧ 0 ∈ S})"
assumes has_vector_derivative_real_power_aux:
"x > 0 ⟹ filterlim (λy. (real_power y c - real_power x (c :: 'a) -
(y - x) *⇩R (c * real_power x (c - 1))) /⇩R
norm (y - x)) (INF S∈{S. open S ∧ 0 ∈ S}. principal S) (at x)"
assumes norm_nat_power: "n > 0 ⟹ norm (nat_power n y) = real n powr (y ∙ 1)"
begin
lemma real_power_diff: "d > 0 ⟹ real_power d (a - b) = real_power d a / real_power d b"
using real_power_add[of d b "a - b"] by (simp add: field_simps)
end
lemma real_power_1_right [simp]: "d > 0 ⟹ real_power d 1 = of_real d"
using real_power_1_right_aux[of d] by (simp add: scaleR_conv_of_real)
lemma has_vector_derivative_real_power [derivative_intros]:
"x > 0 ⟹ ((λy. real_power y c) has_vector_derivative c * real_power x (c - 1)) (at x within A)"
by (rule has_vector_derivative_at_within)
(insert has_vector_derivative_real_power_aux[of x c],
simp add: has_vector_derivative_def has_derivative_def
nhds_def bounded_linear_scaleR_left)
lemma has_field_derivative_nat_power [derivative_intros]:
"n > 0 ⟹ ((λy. nat_power n y) has_field_derivative ln (real n) *⇩R nat_power n x)
(at (x :: 'a :: nat_power_normed_field) within A)"
by (rule has_field_derivative_at_within)
(insert has_field_derivative_nat_power_aux[of n x],
simp only: has_field_derivative_def has_derivative_def netlimit_at,
simp add: nhds_def at_within_def bounded_linear_mult_right)
lemma continuous_on_real_power [continuous_intros]:
"A ⊆ {0<..} ⟹ continuous_on A (λx. real_power x s)"
by (rule continuous_on_vector_derivative has_vector_derivative_real_power)+ auto
instantiation real :: nat_power_normed_field
begin
definition real_power_real :: "real ⇒ real ⇒ real" where
[simp]: "real_power_real = (powr)"
instance proof (standard, goal_cases)
case (7 n x)
hence "((λx. nat_power n x) has_field_derivative ln (real n) *⇩R nat_power n x) (at x)"
by (auto intro!: derivative_eq_intros simp: powr_def)
thus ?case unfolding has_field_derivative_def netlimit_at has_derivative_def
by (simp add: nhds_def at_within_def)
next
case (8 x c)
hence "((λy. real_power y c) has_vector_derivative c * real_power x (c - 1)) (at x)"
by (auto intro!: derivative_eq_intros
simp: has_real_derivative_iff_has_vector_derivative [symmetric])
thus ?case by (simp add: has_vector_derivative_def has_derivative_def nhds_def)
qed (simp_all add: powr_add)
end
instantiation complex :: nat_power_normed_field
begin
definition nat_power_complex :: "nat ⇒ complex ⇒ complex" where
[simp]: "nat_power_complex n z = of_nat n powr z"
definition real_power_complex :: "real ⇒ complex ⇒ complex" where
[simp]: "real_power_complex = (λx y. of_real x powr y)"
instance proof
fix m n :: nat and z :: complex
assume "m > 0" "n > 0"
thus "nat_power (m * n) z = nat_power m z * nat_power n z"
unfolding nat_power_complex_def of_nat_mult by (subst powr_times_real) simp_all
next
fix n :: nat and z :: complex
assume "n > 0"
show "norm (nat_power n z) = real n powr (z ∙ 1)" unfolding nat_power_complex_def
using norm_powr_real_powr[of "of_nat n" z] by simp
next
fix n :: nat and x :: complex assume n: "n > 0"
hence "((λx. nat_power n x) has_field_derivative ln (real n) *⇩R nat_power n x) (at x)"
by (auto intro!: derivative_eq_intros simp: powr_def scaleR_conv_of_real mult_ac)
thus "LIM y inf_class.inf (Inf (principal ` {S. open S ∧ x ∈ S})) (principal (UNIV - {x})).
(nat_power n y - nat_power n x - ln (real n) *⇩R nat_power n x * (y - x)) /⇩R
cmod (y - x) :> (Inf (principal ` {S. open S ∧ 0 ∈ S}))"
unfolding has_field_derivative_def netlimit_at has_derivative_def
by (simp add: nhds_def at_within_def)
next
fix x :: real and c :: complex assume "x > 0"
hence "((λy. real_power y c) has_vector_derivative c * real_power x (c - 1)) (at x)"
by (auto intro!: derivative_eq_intros has_vector_derivative_real_field)
thus "LIM y at x. (real_power y c - real_power x c - (y - x) *⇩R (c * real_power x (c - 1))) /⇩R
norm (y - x) :> INF S∈{S. open S ∧ 0 ∈ S}. principal S"
by (simp add: has_vector_derivative_def has_derivative_def nhds_def)
next
fix n :: nat and x :: real
show "nat_power n (x *⇩R 1 :: complex) = (real n powr x) *⇩R 1"
by (simp add: powr_Reals_eq scaleR_conv_of_real)
qed (auto simp: powr_def exp_add exp_of_nat_mult [symmetric] algebra_simps scaleR_conv_of_real
simp del: Ln_of_nat)
end
lemma nat_power_of_real [simp]:
"nat_power n (of_real x :: 'a :: nat_power_normed_field) = of_real (real n powr x)"
using nat_power_of_real_aux[of n x] by (simp add: scaleR_conv_of_real)
lemma fds_abs_converges_of_real [simp]:
"fds_abs_converges (fds_of_real f)
(of_real s :: 'a :: {nat_power_normed_field,banach}) ⟷ fds_abs_converges f s"
unfolding fds_abs_converges_def
by (subst (1 2) summable_Suc_iff [symmetric]) (simp add: norm_divide norm_nat_power)
lemma eval_fds_of_real [simp]:
assumes "fds_converges f s"
shows "eval_fds (fds_of_real f) (of_real s :: 'a :: {nat_power_normed_field,banach}) =
of_real (eval_fds f s)"
using assms unfolding eval_fds_def by (auto simp: fds_converges_def suminf_of_real)
lemma fds_abs_summable_zeta_iff [simp]:
fixes s :: "'a :: {banach, nat_power_normed_field}"
shows "fds_abs_converges fds_zeta s ⟷ s ∙ 1 > (1 :: real)"
proof -
have "fds_abs_converges fds_zeta s ⟷ summable (λn. real n powr -(s ∙ 1))"
unfolding fds_abs_converges_def
by (intro summable_cong always_eventually)
(auto simp: norm_divide fds_nth_zeta powr_minus norm_nat_power divide_simps)
also have "… ⟷ s ∙ 1 > 1" by (simp add: summable_real_powr_iff)
finally show ?thesis .
qed
lemma fds_abs_summable_zeta:
"(s :: 'a :: {banach, nat_power_normed_field}) ∙ 1 > 1 ⟹ fds_abs_converges fds_zeta s"
by simp
lemma fds_abs_converges_moebius_mu:
fixes s :: "'a :: {banach,nat_power_normed_field}"
assumes "s ∙ 1 > 1"
shows "fds_abs_converges (fds moebius_mu) s"
unfolding fds_abs_converges_def
proof (rule summable_comparison_test, intro exI allI impI)
fix n :: nat
show "norm (norm (fds_nth (fds moebius_mu) n / nat_power n s)) ≤ real n powr (-s ∙ 1)"
by (auto simp: powr_minus divide_simps abs_moebius_mu_le norm_nat_power norm_divide
moebius_mu_def norm_power)
next
from assms show "summable (λn. real n powr (-s ∙ 1))" by (simp add: summable_real_powr_iff)
qed
definition conv_abscissa
:: "'a :: {nat_power,banach,real_normed_field, real_inner} fds ⇒ ereal" where
"conv_abscissa f = (INF s∈{s. fds_converges f s}. ereal (s ∙ 1))"
definition abs_conv_abscissa
:: "'a :: {nat_power,banach,real_normed_field, real_inner} fds ⇒ ereal" where
"abs_conv_abscissa f = (INF s∈{s. fds_abs_converges f s}. ereal (s ∙ 1))"
lemma conv_abscissa_mono:
assumes "⋀s. fds_converges g s ⟹ fds_converges f s"
shows "conv_abscissa f ≤ conv_abscissa g"
unfolding conv_abscissa_def by (rule INF_mono) (use assms in auto)
lemma abs_conv_abscissa_mono:
assumes "⋀s. fds_abs_converges g s ⟹ fds_abs_converges f s"
shows "abs_conv_abscissa f ≤ abs_conv_abscissa g"
unfolding abs_conv_abscissa_def by (rule INF_mono) (use assms in auto)
class dirichlet_series = euclidean_space + real_normed_field + nat_power_normed_field +
assumes one_in_Basis: "1 ∈ Basis"
instance real :: dirichlet_series by standard simp_all
instance complex :: dirichlet_series by standard (simp_all add: Basis_complex_def)
context
assumes "SORT_CONSTRAINT('a :: dirichlet_series)"
begin
lemma fds_abs_converges_Re_le:
fixes f :: "'a fds"
assumes "fds_abs_converges f z" "z ∙ 1 ≤ z' ∙ 1"
shows "fds_abs_converges f z'"
unfolding fds_abs_converges_def
proof (rule summable_comparison_test, intro exI allI impI)
fix n :: nat assume n: "n ≥ 1"
thus "norm (norm (fds_nth f n / nat_power n z')) ≤ norm (fds_nth f n / nat_power n z)"
using assms(2) by (simp add: norm_divide norm_nat_power divide_simps powr_mono mult_left_mono)
qed (insert assms(1), simp add: fds_abs_converges_def)
lemma fds_abs_converges:
assumes "s ∙ 1 > abs_conv_abscissa (f :: 'a fds)"
shows "fds_abs_converges f s"
proof -
from assms obtain s0 where "fds_abs_converges f s0" "s0 ∙ 1 < s ∙ 1"
by (auto simp: INF_less_iff abs_conv_abscissa_def)
with fds_abs_converges_Re_le[OF this(1), of s] this(2) show ?thesis by simp
qed
lemma fds_abs_diverges:
assumes "s ∙ 1 < abs_conv_abscissa (f :: 'a fds)"
shows "¬fds_abs_converges f s"
proof
assume "fds_abs_converges f s"
hence "abs_conv_abscissa f ≤ s ∙ 1" unfolding abs_conv_abscissa_def
by (intro INF_lower) auto
with assms show False by simp
qed
lemma uniformly_Cauchy_eval_fds_aux:
fixes s0 :: "'a :: dirichlet_series"
assumes bounded: "Bseq (λn. ∑k≤n. fds_nth f k / nat_power k s0)"
assumes B: "compact B" "⋀z. z ∈ B ⟹ z ∙ 1 > s0 ∙ 1"
shows "uniformly_Cauchy_on B (λN z. ∑n≤N. fds_nth f n / nat_power n z)"
proof (cases "B = {}")
case False
show ?thesis
proof (rule uniformly_Cauchy_onI', goal_cases)
case (1 ε)
define σ where "σ = Inf ((λs. s ∙ 1) ` B)"
have σ_le: "s ∙ 1 ≥ σ" if "s ∈ B" for s
unfolding σ_def using that
by (intro cInf_lower bounded_inner_imp_bdd_below compact_imp_bounded B) auto
have "σ ∈ ((λs. s ∙ 1) ` B)"
unfolding σ_def using B ‹B ≠ {}›
by (intro closed_contains_Inf bounded_inner_imp_bdd_below compact_imp_bounded B
compact_imp_closed compact_continuous_image continuous_intros) auto
with B(2) have σ_gt: "σ > s0 ∙ 1" by auto
define δ where "δ = σ - s0 ∙ 1"
have "bounded B" by (rule compact_imp_bounded) fact
then obtain norm_B_aux where norm_B_aux: "⋀s. s ∈ B ⟹ norm s ≤ norm_B_aux"
by (auto simp: bounded_iff)
define norm_B where "norm_B = norm_B_aux + norm s0"
from norm_B_aux have norm_B: "norm (s - s0) ≤ norm_B" if "s ∈ B" for s
using norm_triangle_ineq4[of s s0] norm_B_aux[OF that] by (simp add: norm_B_def)
then have "0 ≤ norm_B"
by (meson ‹σ ∈ (λs. s ∙ 1) ` B› imageE norm_ge_zero order.trans)
define A where "A = sum_upto (λk. fds_nth f k / nat_power k s0)"
from bounded obtain C_aux where C_aux: "⋀n. norm (∑k≤n. fds_nth f k / nat_power k s0) ≤ C_aux"
by (auto simp: Bseq_def)
define C where "C = max C_aux 1"
have C_pos: "C > 0" by (simp add: C_def)
have C: "norm (A x) ≤ C" for x
proof -
have "A x = (∑k≤nat ⌊x⌋. fds_nth f k / nat_power k s0)"
unfolding A_def sum_upto_altdef by (intro sum.mono_neutral_left) auto
also have "norm … ≤ C_aux" by (rule C_aux)
also have "… ≤ C" by (simp add: C_def)
finally show ?thesis .
qed
have "(λm. 2 * C * (1 + norm_B / δ) * real m powr (-δ)) ⇢ 0" unfolding δ_def using σ_gt
by (intro tendsto_mult_right_zero tendsto_neg_powr filterlim_real_sequentially) simp_all
from order_tendstoD(2)[OF this ‹ε > 0›] obtain M where
M: "⋀m. m ≥ M ⟹ 2 * C * (1 + norm_B / δ) * real m powr - δ < ε"
by (auto simp: eventually_at_top_linorder)
show ?case
proof (intro exI[of _ "max M 1"] ballI allI impI, goal_cases)
case (1 s m n)
from 1 have s: "s ∙ 1 > s0 ∙ 1" using B(2)[of s] by simp
have mn: "m ≥ M" "m < n" "m > 0" "n > 0" using 1 by (simp_all add: )
have "dist (∑n≤m. fds_nth f n / nat_power n s) (∑n≤n. fds_nth f n / nat_power n s) =
dist (∑n≤n. fds_nth f n / nat_power n s) (∑n≤m. fds_nth f n / nat_power n s)"
by (simp add: dist_commute)
also from 1 have "… = norm (∑k∈{..n}-{..m}. fds_nth f k / nat_power k s)"
by (subst Groups_Big.sum_diff) (simp_all add: dist_norm)
also from 1 have "{..n} - {..m} = real -` {real m<..real n}" by auto
also have "(∑k∈…. fds_nth f k / nat_power k s) =
(∑k∈…. fds_nth f k / nat_power k s0 * real_power (real k) (s0 - s))"
(is "_ = ?S") by (intro sum.cong refl) (simp_all add: nat_power_diff real_power_nat_power)
also have *: "((λt. A t * ((s0 - s) * real_power t (s0 - s - 1))) has_integral
(A (real n) * real_power n (s0 - s) - A (real m) * real_power m (s0 - s) - ?S))
{real m..real n}" (is "(?h has_integral _) _") unfolding A_def using mn
by (intro partial_summation_strong[of "{}"])
(auto intro!: derivative_eq_intros continuous_intros)
hence "?S = A (real n) * nat_power n (s0 - s) - A (real m) * nat_power m (s0 - s) -
integral {real m..real n} ?h"
using mn by (simp add: has_integral_iff real_power_nat_power)
also have "norm … ≤ norm (A (real n) * nat_power n (s0 - s)) +
norm (A (real m) * nat_power m (s0 - s)) + norm (integral {real m..real n} ?h)"
by (intro order.trans[OF norm_triangle_ineq4] add_right_mono order.refl)
also have "norm (A (real n) * nat_power n (s0 - s)) ≤ C * nat_power m ((s0 - s) ∙ 1)"
using mn ‹s ∈ B› C_pos s
by (auto simp: norm_mult norm_nat_power algebra_simps intro!: mult_mono C powr_mono2')
also have "norm (A (real m) * nat_power m (s0 - s)) ≤ C * nat_power m ((s0 - s) ∙ 1)"
using mn by (auto simp: norm_mult norm_nat_power intro!: mult_mono C)
also have "norm (integral {real m..real n} ?h) ≤
integral {real m..real n} (λt. C * (norm (s0 - s) * t powr ((s0 - s) ∙ 1 - 1)))"
proof (intro integral_norm_bound_integral ballI, goal_cases)
case 1
with * show ?case by (simp add: has_integral_iff)
next
case 2
from mn show ?case by (auto intro!: integrable_continuous_real continuous_intros)
next
case (3 t)
thus ?case unfolding norm_mult using C_pos mn
by (intro mult_mono C) (auto simp: norm_real_power dot_square_norm algebra_simps)
qed
also have "… = C * norm (s0 - s) * integral {real m..real n} (λt. t powr ((s0 - s) ∙ 1 - 1))"
by (simp add: algebra_simps dot_square_norm)
also {
have "((λt. t powr ((s0 - s) ∙ 1 - 1)) has_integral
(real n powr ((s0 - s) ∙ 1) / ((s0 - s) ∙ 1) -
real m powr ((s0 - s) ∙ 1) / ((s0 - s) ∙ 1))) {m..n}"
(is "(?l has_integral ?I) _") using mn s
by (intro fundamental_theorem_of_calculus)
(auto intro!: derivative_eq_intros
simp: has_real_derivative_iff_has_vector_derivative [symmetric] inner_diff_left)
hence "integral {real m..real n} ?l = ?I" by (simp add: has_integral_iff)
also have "… ≤ -(real m powr ((s0 - s) ∙ 1) / ((s0 - s) ∙ 1))" using s mn
by (simp add: divide_simps inner_diff_left)
also have "… = 1 * (real m powr ((s0 - s) ∙ 1) / ((s - s0) ∙ 1))"
using s by (simp add: field_simps inner_diff_left)
also have "… ≤ 2 * (real m powr ((s0 - s) ∙ 1) / ((s - s0) ∙ 1))" using mn s
by (intro mult_right_mono divide_nonneg_pos) (simp_all add: inner_diff_left)
finally have "integral {m..n} ?l ≤ …" .
}
hence "C * norm (s0 - s) * integral {real m..real n} (λt. t powr ((s0 - s) ∙ 1 - 1)) ≤
C * norm (s0 - s) * (2 * (real m powr ((s0 - s) ∙ 1) / ((s - s0) ∙ 1)))"
using C_pos mn
by (intro mult_mono mult_nonneg_nonneg integral_nonneg
integrable_continuous_real continuous_intros) auto
also have "C * nat_power m ((s0 - s) ∙ 1) + C * nat_power m ((s0 - s) ∙ 1) + … =
2 * C * nat_power m ((s0 - s) ∙ 1) * (1 + norm (s - s0) / ((s - s0) ∙ 1))"
by (simp add: algebra_simps norm_minus_commute)
also have "… ≤ 2 * C * nat_power m (-δ) * (1 + norm_B / δ)"
using C_pos s mn σ_le[of s] ‹s ∈ B› σ_gt ‹0 ≤ norm_B›
unfolding nat_power_real_def δ_def
by (intro mult_mono powr_mono frac_le add_mono norm_B; simp add: inner_diff_left)
also have "… = 2 * C * (1 + norm_B / δ) * real m powr (-δ)" by simp
also from ‹m ≥ M› have "… < ε" by (rule M)
finally show ?case by - simp_all
qed
qed
qed (auto simp: uniformly_Cauchy_on_def)
lemma uniformly_convergent_eval_fds_aux:
assumes "Bseq (λn. ∑k≤n. fds_nth f k / nat_power k (s0 :: 'a))"
assumes B: "compact B" "⋀z. z ∈ B ⟹ z ∙ 1 > s0 ∙ 1"
shows "uniformly_convergent_on B (λN z. ∑n≤N. fds_nth f n / nat_power n z)"
by (rule Cauchy_uniformly_convergent uniformly_Cauchy_eval_fds_aux assms)+
lemma uniformly_convergent_eval_fds_aux':
assumes conv: "fds_converges f (s0 :: 'a)"
assumes B: "compact B" "⋀z. z ∈ B ⟹ z ∙ 1 > s0 ∙ 1"
shows "uniformly_convergent_on B (λN z. ∑n≤N. fds_nth f n / nat_power n z)"
proof (rule uniformly_convergent_eval_fds_aux)
from conv have "convergent (λn. ∑k≤n. fds_nth f k / nat_power k s0)"
by (simp add: fds_converges_def summable_iff_convergent')
thus "Bseq (λn. ∑k≤n. fds_nth f k / nat_power k s0)" by (rule convergent_imp_Bseq)
qed (insert assms, auto)
lemma bounded_partial_sums_imp_fps_converges:
fixes s0 :: "'a :: dirichlet_series"
assumes "Bseq (λn. ∑k≤n. fds_nth f k / nat_power k s0)" and "s ∙ 1 > s0 ∙ 1"
shows "fds_converges f s"
proof -
have "uniformly_convergent_on {s} (λN z. ∑n≤N. fds_nth f n / nat_power n z)" using assms(2)
by (intro uniformly_convergent_eval_fds_aux[OF assms(1)]) auto
thus ?thesis
by (auto simp: fds_converges_def summable_iff_convergent'
dest: uniformly_convergent_imp_convergent)
qed
theorem fds_converges_Re_le:
assumes "fds_converges f (s0 :: 'a)" "s ∙ 1 > s0 ∙ 1"
shows "fds_converges f s"
proof -
have "uniformly_convergent_on {s} (λN z. ∑n≤N. fds_nth f n / nat_power n z)"
by (rule uniformly_convergent_eval_fds_aux' assms)+ (insert assms(2), auto)
then obtain l where "uniform_limit {s} (λN z. ∑n≤N. fds_nth f n / nat_power n z) l at_top"
by (auto simp: uniformly_convergent_on_def)
from tendsto_uniform_limitI[OF this, of s]
have "(λn. fds_nth f n / nat_power n s) sums l s" unfolding sums_def'
by (simp add: atLeast0AtMost)
thus ?thesis by (simp add: fds_converges_def sums_iff)
qed
lemma fds_converges:
assumes "s ∙ 1 > conv_abscissa (f :: 'a fds)"
shows "fds_converges f s"
proof -
from assms obtain s0 where "fds_converges f s0" "s0 ∙ 1 < s ∙ 1"
by (auto simp: INF_less_iff conv_abscissa_def)
with fds_converges_Re_le[OF this(1), of s] this(2) show ?thesis by simp
qed
lemma fds_diverges:
assumes "s ∙ 1 < conv_abscissa (f :: 'a fds)"
shows "¬fds_converges f s"
proof
assume "fds_converges f s"
hence "conv_abscissa f ≤ s ∙ 1" unfolding conv_abscissa_def
by (intro INF_lower) auto
with assms show False by simp
qed
theorem fds_converges_imp_abs_converges:
assumes "fds_converges (f :: 'a fds) s" "s' ∙ 1 > s ∙ 1 + 1"
shows "fds_abs_converges f s'"
unfolding fds_abs_converges_def
proof (rule summable_comparison_test_ev)
from assms(2) show "summable (λn. real n powr ((s - s') ∙ 1))"
by (subst summable_real_powr_iff) (simp_all add: inner_diff_left)
next
from assms(1) have "(λn. fds_nth f n / nat_power n s) ⇢ 0"
unfolding fds_converges_def by (rule summable_LIMSEQ_zero)
from tendsto_norm[OF this] have "(λn. norm (fds_nth f n / nat_power n s)) ⇢ 0" by simp
hence "eventually (λn. norm (fds_nth f n / nat_power n s) < 1) at_top"
by (rule order_tendstoD) simp_all
thus "eventually (λn. norm (norm (fds_nth f n / nat_power n s')) ≤
real n powr ((s - s') ∙ 1)) at_top"
proof eventually_elim
case (elim n)
thus ?case
proof (cases "n = 0")
case False
have "norm (fds_nth f n / nat_power n s') =
norm (fds_nth f n) / real n powr (s' ∙ 1)" using False
by (simp add: norm_divide norm_nat_power)
also have "… = norm (fds_nth f n / nat_power n s) / real n powr ((s' - s) ∙ 1)" using False
by (simp add: norm_divide norm_nat_power inner_diff_left powr_diff)
also have "… ≤ 1 / real n powr ((s' - s) ∙ 1)" using elim
by (intro divide_right_mono elim) simp_all
also have "… = real n powr ((s - s') ∙ 1)" using False
by (simp add: field_simps inner_diff_left powr_diff)
finally show ?thesis by simp
qed simp_all
qed
qed
lemma conv_le_abs_conv_abscissa: "conv_abscissa f ≤ abs_conv_abscissa f"
unfolding conv_abscissa_def abs_conv_abscissa_def
by (intro INF_superset_mono) auto
lemma conv_abscissa_PInf_iff: "conv_abscissa f = ∞ ⟷ (∀s. ¬fds_converges f s)"
unfolding conv_abscissa_def by (subst Inf_eq_PInfty) auto
lemma conv_abscissa_PInfI [intro]: "(⋀s. ¬fds_converges f s) ⟹ conv_abscissa f = ∞"
by (subst conv_abscissa_PInf_iff) auto
lemma conv_abscissa_MInf_iff: "conv_abscissa (f :: 'a fds) = -∞ ⟷ (∀s. fds_converges f s)"
proof safe
assume *: "∀s. fds_converges f s"
have "conv_abscissa f ≤ B" for B :: real
using spec[OF *, of "of_real B"] fds_diverges[of "of_real B" f]
by (cases "conv_abscissa f ≤ B") simp_all
thus "conv_abscissa f = -∞" by (rule ereal_bot)
qed (auto intro: fds_converges)
lemma conv_abscissa_MInfI [intro]: "(⋀s. fds_converges (f::'a fds) s) ⟹ conv_abscissa f = -∞"
by (subst conv_abscissa_MInf_iff) auto
lemma abs_conv_abscissa_PInf_iff: "abs_conv_abscissa f = ∞ ⟷ (∀s. ¬fds_abs_converges f s)"
unfolding abs_conv_abscissa_def by (subst Inf_eq_PInfty) auto
lemma abs_conv_abscissa_PInfI [intro]: "(⋀s. ¬fds_converges f s) ⟹ abs_conv_abscissa f = ∞"
by (subst abs_conv_abscissa_PInf_iff) auto
lemma abs_conv_abscissa_MInf_iff:
"abs_conv_abscissa (f :: 'a fds) = -∞ ⟷ (∀s. fds_abs_converges f s)"
proof safe
assume *: "∀s. fds_abs_converges f s"
have "abs_conv_abscissa f ≤ B" for B :: real
using spec[OF *, of "of_real B"] fds_abs_diverges[of "of_real B" f]
by (cases "abs_conv_abscissa f ≤ B") simp_all
thus "abs_conv_abscissa f = -∞" by (rule ereal_bot)
qed (auto intro: fds_abs_converges)
lemma abs_conv_abscissa_MInfI [intro]:
"(⋀s. fds_abs_converges (f::'a fds) s) ⟹ abs_conv_abscissa f = -∞"
by (subst abs_conv_abscissa_MInf_iff) auto
lemma conv_abscissa_geI:
assumes "⋀c'. ereal c' < c ⟹ ∃s. s ∙ 1 = c' ∧ ¬fds_converges f s"
shows "conv_abscissa (f :: 'a fds) ≥ c"
proof (rule ccontr)
assume "¬conv_abscissa f ≥ c"
hence "c > conv_abscissa f" by simp
from ereal_dense2[OF this] obtain c' where "c > ereal c'" "c' > conv_abscissa f" by auto
moreover from assms[OF this(1)] obtain s where "s ∙ 1 = c'" "¬fds_converges f s" by blast
ultimately show False using fds_converges[of f s] by auto
qed
lemma conv_abscissa_leI:
assumes "⋀c'. ereal c' > c ⟹ ∃s. s ∙ 1 = c' ∧ fds_converges f s"
shows "conv_abscissa (f :: 'a fds) ≤ c"
proof (rule ccontr)
assume "¬conv_abscissa f ≤ c"
hence "c < conv_abscissa f" by simp
from ereal_dense2[OF this] obtain c' where "c < ereal c'" "c' < conv_abscissa f" by auto
moreover from assms[OF this(1)] obtain s where "s ∙ 1 = c'" "fds_converges f s" by blast
ultimately show False using fds_diverges[of s f] by auto
qed
lemma abs_conv_abscissa_geI:
assumes "⋀c'. ereal c' < c ⟹ ∃s. s ∙ 1 = c' ∧ ¬fds_abs_converges f s"
shows "abs_conv_abscissa (f :: 'a fds) ≥ c"
proof (rule ccontr)
assume "¬abs_conv_abscissa f ≥ c"
hence "c > abs_conv_abscissa f" by simp
from ereal_dense2[OF this] obtain c' where "c > ereal c'" "c' > abs_conv_abscissa f" by auto
moreover from assms[OF this(1)] obtain s where "s ∙ 1 = c'" "¬fds_abs_converges f s" by blast
ultimately show False using fds_abs_converges[of f s] by auto
qed
lemma abs_conv_abscissa_leI:
assumes "⋀c'. ereal c' > c ⟹ ∃s. s ∙ 1 = c' ∧ fds_abs_converges f s"
shows "abs_conv_abscissa (f :: 'a fds) ≤ c"
proof (rule ccontr)
assume "¬abs_conv_abscissa f ≤ c"
hence "c < abs_conv_abscissa f" by simp
from ereal_dense2[OF this] obtain c' where "c < ereal c'" "c' < abs_conv_abscissa f" by auto
moreover from assms[OF this(1)] obtain s where "s ∙ 1 = c'" "fds_abs_converges f s" by blast
ultimately show False using fds_abs_diverges[of s f] by auto
qed
lemma conv_abscissa_leI_weak:
assumes "⋀x. ereal x > d ⟹ fds_converges f (of_real x)"
shows "conv_abscissa (f :: 'a fds) ≤ d"
proof (rule conv_abscissa_leI)
fix x assume "d < ereal x"
from assms[OF this] show "∃s. s ∙ 1 = x ∧ fds_converges f s"
by (intro exI[of _ "of_real x"]) auto
qed
lemma abs_conv_abscissa_leI_weak:
assumes "⋀x. ereal x > d ⟹ fds_abs_converges f (of_real x)"
shows "abs_conv_abscissa (f :: 'a fds) ≤ d"
proof (rule abs_conv_abscissa_leI)
fix x assume "d < ereal x"
from assms[OF this] show "∃s. s ∙ 1 = x ∧ fds_abs_converges f s"
by (intro exI[of _ "of_real x"]) auto
qed
lemma conv_abscissa_truncate [simp]:
"conv_abscissa (fds_truncate m (f :: 'a fds)) = -∞"
by (auto simp: conv_abscissa_MInf_iff)
lemma abs_conv_abscissa_truncate [simp]:
"abs_conv_abscissa (fds_truncate m (f :: 'a fds)) = -∞"
by (auto simp: abs_conv_abscissa_MInf_iff)
theorem abs_conv_le_conv_abscissa_plus_1: "abs_conv_abscissa (f :: 'a fds) ≤ conv_abscissa f + 1"
proof (rule abs_conv_abscissa_leI)
fix c assume less: "conv_abscissa f + 1 < ereal c"
define c' where "c' = (if conv_abscissa f = -∞ then c - 2
else (c - 1 + real_of_ereal (conv_abscissa f)) / 2)"
from less have c': "conv_abscissa f < ereal c' ∧ c' < c - 1"
by (cases "conv_abscissa f") (simp_all add: c'_def field_simps)
from c' have "fds_converges f (of_real c')"
by (intro fds_converges) (simp_all add: inner_diff_left dot_square_norm)
hence "fds_abs_converges f (of_real c)"
by (rule fds_converges_imp_abs_converges) (insert c', simp_all)
thus "∃s. s ∙ 1 = c ∧ fds_abs_converges f s"
by (intro exI[of _ "of_real c"]) auto
qed
lemma uniformly_convergent_eval_fds:
assumes B: "compact B" "⋀z. z ∈ B ⟹ z ∙ 1 > conv_abscissa (f :: 'a fds)"
shows "uniformly_convergent_on B (λN z. ∑n≤N. fds_nth f n / nat_power n z)"
proof (cases "B = {}")
case False
define σ where "σ = Inf ((λs. s ∙ 1) ` B)"
have σ_le: "s ∙ 1 ≥ σ" if "s ∈ B" for s
unfolding σ_def using that
by (intro cInf_lower bounded_inner_imp_bdd_below compact_imp_bounded B) auto
have "σ ∈ ((λs. s ∙ 1) ` B)"
unfolding σ_def using B ‹B ≠ {}›
by (intro closed_contains_Inf bounded_inner_imp_bdd_below compact_imp_bounded B
compact_imp_closed compact_continuous_image continuous_intros) auto
with B(2) have σ_gt: "σ > conv_abscissa f" by auto
define s where "s = (if conv_abscissa f = -∞ then σ - 1 else
(σ + real_of_ereal (conv_abscissa f)) / 2)"
from σ_gt have s: "conv_abscissa f < s ∧ s < σ"
by (cases "conv_abscissa f") (auto simp: s_def)
show ?thesis using s ‹compact B›
by (intro uniformly_convergent_eval_fds_aux'[of f "of_real s"] fds_converges)
(auto dest: σ_le)
qed auto
corollary uniformly_convergent_eval_fds':
assumes B: "compact B" "⋀z. z ∈ B ⟹ z ∙ 1 > conv_abscissa (f :: 'a fds)"
shows "uniformly_convergent_on B (λN z. ∑n<N. fds_nth f n / nat_power n z)"
proof -
from uniformly_convergent_eval_fds[OF assms] obtain l where
"uniform_limit B (λN z. ∑n≤N. fds_nth f n / nat_power n z) l at_top"
by (auto simp: uniformly_convergent_on_def)
also have "(λN z. ∑n≤N. fds_nth f n / nat_power n z) =
(λN z. ∑n<Suc N. fds_nth f n / nat_power n z)"
by (simp only: lessThan_Suc_atMost)
finally have "uniform_limit B (λN z. ∑n<N. fds_nth f n / nat_power n z) l at_top"
unfolding uniform_limit_iff by (subst (asm) eventually_sequentially_Suc)
thus ?thesis by (auto simp: uniformly_convergent_on_def)
qed
subsection ‹Derivative of a Dirichlet series›
lemma fds_converges_deriv_aux:
assumes conv: "fds_converges f (s0 :: 'a)" and gt: "s ∙ 1 > s0 ∙ 1"
shows "fds_converges (fds_deriv f) s"
proof -
have "Cauchy (λn. ∑k≤n. (-ln (real k) *⇩R fds_nth f k) / nat_power k s)"
proof (rule CauchyI', goal_cases)
case (1 ε)
define δ where "δ = s ∙ 1 - s0 ∙ 1"
define δ' where "δ' = δ / 2"
from gt have δ_pos: "δ > 0" by (simp add: δ_def)
define A where "A = sum_upto (λk. fds_nth f k / nat_power k s0)"
from conv have "convergent (λn. ∑k≤n. fds_nth f k / nat_power k s0)"
by (simp add: fds_converges_def summable_iff_convergent')
hence "Bseq (λn. ∑k≤n. fds_nth f k / nat_power k s0)" by (rule convergent_imp_Bseq)
then obtain C_aux where C_aux: "⋀n. norm (∑k≤n. fds_nth f k / nat_power k s0) ≤ C_aux"
by (auto simp: Bseq_def)
define C where "C = max C_aux 1"
have C_pos: "C > 0" by (simp add: C_def)
have C: "norm (A x) ≤ C" for x
proof -
have "A x = (∑k≤nat ⌊x⌋. fds_nth f k / nat_power k s0)"
unfolding A_def sum_upto_altdef by (intro sum.mono_neutral_left) auto
also have "norm … ≤ C_aux" by (rule C_aux)
also have "… ≤ C" by (simp add: C_def)
finally show ?thesis .
qed
define C' where "C' = 2 * C + C * (norm (s0 - s) * (1 + 1 / δ) + 1) / δ"
have "(λm. C' * real m powr (-δ')) ⇢ 0" unfolding δ'_def using gt δ_pos
by (intro tendsto_mult_right_zero tendsto_neg_powr filterlim_real_sequentially) simp_all
from order_tendstoD(2)[OF this ‹ε > 0›] obtain M1 where
M1: "⋀m. m ≥ M1 ⟹ C' * real m powr - δ' < ε"
by (auto simp: eventually_at_top_linorder)
have "((λx. ln (real x) / real x powr δ') ⤏ 0) at_top" using δ_pos
by (intro lim_ln_over_power) (simp_all add: δ'_def)
from order_tendstoD(2)[OF this zero_less_one] eventually_gt_at_top[of "1::nat"]
have "eventually (λn. ln (real n) ≤ n powr δ') at_top" by eventually_elim simp_all
then obtain M2 where M2: "⋀n. n ≥ M2 ⟹ ln (real n) ≤ n powr δ'"
by (auto simp: eventually_at_top_linorder)
let ?f' = "λk. -ln (real k) *⇩R fds_nth f k"
show ?case
proof (intro exI[of _ "max (max M1 M2) 1"] allI impI, goal_cases)
case (1 m n)
hence mn: "m ≥ M1" "m ≥ M2" "m > 0" "m < n" by simp_all
define g :: "real ⇒ 'a" where "g = (λt. real_power t (s0 - s) * of_real (ln t))"
define g' :: "real ⇒ 'a"
where "g' = (λt. real_power t (s0 - s - 1) * ((s0 - s) * of_real (ln t) + 1))"
define norm_g' :: "real ⇒ real"
where "norm_g' = (λt. t powr (-δ - 1) * (norm (s0 - s) * ln t + 1))"
define norm_g :: "real ⇒ real"
where "norm_g = (λt. -(t powr -δ) * (norm (s0 - s) * (δ * ln t + 1) + δ) / δ^2)"
have g_g': "(g has_vector_derivative g' t) (at t)" if "t ∈ {real m..real n}" for t
using mn that by (auto simp: g_def g'_def real_power_diff field_simps real_power_add
intro!: derivative_eq_intros)
have [continuous_intros]: "continuous_on {real m..real n} g" using mn
by (auto simp: g_def intro!: continuous_intros)
let ?S = "∑k∈real -` {real m<..real n}. fds_nth f k / nat_power k s0 * g k"
have "dist (∑k≤m. ?f' k / nat_power k s) (∑k≤n. ?f' k / nat_power k s) =
norm (∑k∈{..n} - {..m}. fds_nth f k / nat_power k s * of_real (ln (real k)))"
using mn by (subst sum_diff)
(simp_all add: dist_norm norm_minus_commute sum_negf scaleR_conv_of_real mult_ac)
also have "{..n} - {..m} = real -` {real m<..real n}" by auto
also have "(∑k∈…. fds_nth f k / nat_power k s * of_real (ln (real k))) =
(∑k∈…. fds_nth f k / nat_power k s0 * g k)" using mn unfolding g_def
by (intro sum.cong refl) (auto simp: real_power_nat_power field_simps nat_power_diff)
also have *: "((λt. A t * g' t) has_integral
(A (real n) * g n - A (real m) * g m - ?S))
{real m..real n}" (is "(?h has_integral _) _") unfolding A_def using mn
by (intro partial_summation_strong[of "{}"])
(auto intro!: g_g' simp: field_simps continuous_intros)
hence "?S = A (real n) * g n - A (real m) * g m - integral {real m..real n} ?h"
using mn by (simp add: has_integral_iff field_simps)
also have "norm … ≤ norm (A (real n) * g n) + norm (A (real m) * g m) +
norm (integral {real m..real n} ?h)"
by (intro order.trans[OF norm_triangle_ineq4] add_right_mono order.refl)
also have "norm (A (real n) * g n) ≤ C * norm (g n)"
unfolding norm_mult using mn C_pos by (intro mult_mono C) auto
also have "norm (g n) ≤ n powr -δ * n powr δ'" using mn M2[of n]
by (simp add: g_def norm_real_power norm_mult δ_def inner_diff_left)
also have "… = n powr -δ'" using mn
by (simp add: δ'_def powr_minus field_simps powr_add [symmetric])
also have "norm (A (real m) * g m) ≤ C * norm (g m)"
unfolding norm_mult using mn C_pos by (intro mult_mono C) auto
also have "norm (g m) ≤ m powr -δ * m powr δ'" using mn M2[of m]
by (simp add: g_def norm_real_power norm_mult δ_def inner_diff_left)
also have "… = m powr -δ'" using mn
by (simp add: δ'_def powr_minus field_simps powr_add [symmetric])
also have "C * real n powr - δ' ≤ C * real m powr - δ'" using δ_pos mn C_pos
by (intro mult_left_mono powr_mono2') (simp_all add: δ'_def)
also have "… + … = 2 * …" by simp
also have "norm (integral {m..n} ?h) ≤ integral {m..n} (λt. C * norm_g' t)"
proof (intro integral_norm_bound_integral ballI, goal_cases)
case 1
with * show ?case by (simp add: has_integral_iff)
next
case 2
from mn show ?case
by (auto intro!: integrable_continuous_real continuous_intros simp: norm_g'_def)
next
case (3 t)
have "norm (g' t) ≤ norm_g' t" unfolding g'_def norm_g'_def using 3 mn
unfolding norm_mult
by (intro mult_mono order.trans[OF norm_triangle_ineq])
(auto simp: norm_real_power inner_diff_left dot_square_norm norm_mult δ_def
intro!: mult_left_mono)
thus ?case unfolding norm_mult using C_pos mn
by (intro mult_mono C) simp_all
qed
also have "… = C * integral {m..n} norm_g'"
unfolding norm_g'_def by (simp add: norm_g'_def δ_def inner_diff_left)
also {
have "(norm_g' has_integral (norm_g n - norm_g m)) {m..n}"
unfolding norm_g'_def norm_g_def power2_eq_square using mn δ_pos
by (intro fundamental_theorem_of_calculus)
(auto simp: has_real_derivative_iff_has_vector_derivative [symmetric]
field_simps powr_diff intro!: derivative_eq_intros)
hence "integral {m..n} norm_g' = norm_g n - norm_g m" by (simp add: has_integral_iff)
also have "norm_g n ≤ 0" unfolding norm_g_def using δ_pos mn
by (intro divide_nonpos_pos mult_nonpos_nonneg add_nonneg_nonneg mult_nonneg_nonneg)
simp_all
hence "norm_g n - norm_g m ≤ -norm_g m" by simp
also have "… = real m powr -δ * ln (real m) * (norm (s0 - s)) / δ +
real m powr -δ * ((norm (s0 - s) / δ + 1) / δ)" using δ_pos
by (simp add: field_simps norm_g_def power2_eq_square)
also {
have "ln (real m) ≤ real m powr δ'" using M2[of m] mn by simp
also have "real m powr -δ * … = real m powr -δ'"
by (simp add: powr_add [symmetric] δ'_def)
finally have "real m powr -δ * ln (real m) * (norm (s0 - s)) / δ ≤
… * (norm (s0 - s)) / δ" using δ_pos
by (intro divide_right_mono mult_right_mono) (simp_all add: mult_left_mono)
}
also have "real m powr -δ * ((norm (s0 - s) / δ + 1) / δ) ≤
real m powr -δ' * ((norm (s0 - s) / δ + 1) / δ)" using mn δ_pos
by (intro mult_right_mono powr_mono) (simp_all add: δ'_def)
also have "real m powr - δ' * norm (s0 - s) / δ + … =
real m powr -δ' * (norm (s0 - s) * (1 + 1 / δ) + 1) / δ" using δ_pos
by (simp add: field_simps power2_eq_square)
finally have "integral {real m..real n} norm_g' ≤
real m powr - δ' * (norm (s0 - s) * (1 + 1 / δ) + 1) / δ" by - simp_all
}
also have "2 * (C * m powr - δ') + C * (m powr - δ' * (norm (s0 - s) * (1 + 1 / δ) + 1) / δ) =
C' * m powr -δ'" by (simp add: algebra_simps C'_def)
also have "… < ε" using M1[of m] mn by simp
finally show ?case using C_pos by - simp_all
qed
qed
from Cauchy_convergent[OF this]
show ?thesis by (simp add: summable_iff_convergent' fds_converges_def fds_nth_deriv)
qed
theorem
assumes "s ∙ 1 > conv_abscissa (f :: 'a fds)"
shows fds_converges_deriv: "fds_converges (fds_deriv f) s"
and has_field_derivative_eval_fds [derivative_intros]:
"(eval_fds f has_field_derivative eval_fds (fds_deriv f) s) (at s within A)"
proof -
define s1 :: real where
"s1 = (if conv_abscissa f = -∞ then s ∙ 1 - 2 else
(s ∙ 1 * 1 / 3 + real_of_ereal (conv_abscissa f) * 2 / 3))"
define s2 :: real where
"s2 = (if conv_abscissa f = -∞ then s ∙ 1 - 1 else
(s ∙ 1 * 2 / 3 + real_of_ereal (conv_abscissa f) * 1 / 3))"
from assms have s: "conv_abscissa f < s1 ∧ s1 < s2 ∧ s2 < s ∙ 1"
by (cases "conv_abscissa f") (auto simp: s1_def s2_def field_simps)
from s have *: "fds_converges f (of_real s1)" by (intro fds_converges) simp_all
thus conv': "fds_converges (fds_deriv f) s"
by (rule fds_converges_deriv_aux) (insert s, simp_all)
from * have conv: "fds_converges (fds_deriv f) (of_real s2)"
by (rule fds_converges_deriv_aux) (insert s, simp_all)
define δ :: real where "δ = (s ∙ 1 - s2) / 2"
from s have δ_pos: "δ > 0" by (simp add: δ_def)
have "uniformly_convergent_on (cball s δ)
(λn s. ∑k≤n. fds_nth (fds_deriv f) k / nat_power k s)"
proof (intro uniformly_convergent_eval_fds_aux'[OF conv])
fix s'' :: 'a assume s'': "s'' ∈ cball s δ"
have "dist (s ∙ 1) (s'' ∙ 1) ≤ dist s s''"
by (intro Euclidean_dist_upper) (simp_all add: one_in_Basis)
also from s'' have "… ≤ δ" by simp
finally show "s'' ∙ 1 > (of_real s2 :: 'a) ∙ 1" using s
by (auto simp: δ_def dist_real_def abs_if split: if_splits)
qed (insert δ_pos, auto)
then obtain l where
"uniform_limit (cball s δ) (λn s. ∑k≤n. fds_nth (fds_deriv f) k / nat_power k s) l at_top"
by (auto simp: uniformly_convergent_on_def)
also have "(λn s. ∑k≤n. fds_nth (fds_deriv f) k / nat_power k s) =
(λn s. ∑k<Suc n. fds_nth (fds_deriv f) k / nat_power k s)"
by (simp only: lessThan_Suc_atMost)
finally have "uniform_limit (cball s δ) (λn s. ∑k<n. fds_nth (fds_deriv f) k / nat_power k s)
l at_top"
unfolding uniform_limit_iff by (subst (asm) eventually_sequentially_Suc)
hence *: "uniformly_convergent_on (cball s δ)
(λn s. ∑k<n. fds_nth (fds_deriv f) k / nat_power k s)"
unfolding uniformly_convergent_on_def by blast
have "(eval_fds f has_field_derivative eval_fds (fds_deriv f) s) (at s)"
unfolding eval_fds_def
proof (rule has_field_derivative_series'(2)[OF _ _ *])
show "s ∈ cball s δ" "s ∈ interior (cball s δ)" using s by (simp_all add: δ_def)
show "summable (λn. fds_nth f n / nat_power n s)"
using assms fds_converges[of f s] by (simp add: fds_converges_def)
next
fix s' :: 'a and n :: nat
show "((λs. fds_nth f n / nat_power n s) has_field_derivative
fds_nth (fds_deriv f) n / nat_power n s') (at s' within cball s δ)"
by (cases "n = 0")
(simp, auto intro!: derivative_eq_intros simp: fds_nth_deriv field_simps)
qed (auto simp: fds_nth_deriv intro!: derivative_eq_intros)
thus "(eval_fds f has_field_derivative eval_fds (fds_deriv f) s) (at s within A)"
by (rule has_field_derivative_at_within)
qed
lemmas has_field_derivative_eval_fds' [derivative_intros] =
DERIV_chain2[OF has_field_derivative_eval_fds]
lemma continuous_eval_fds [continuous_intros]:
assumes "s ∙ 1 > conv_abscissa f"
shows "continuous (at s within A) (eval_fds (f :: 'a :: dirichlet_series fds))"
proof -
have "isCont (eval_fds f) s"
by (rule has_field_derivative_eval_fds DERIV_isCont assms)+
thus ?thesis by (rule continuous_within_subset) auto
qed
lemma continuous_eval_fds' [continuous_intros]:
fixes f :: "'a :: dirichlet_series fds"
assumes "continuous (at s within A) g" "g s ∙ 1 > conv_abscissa f"
shows "continuous (at s within A) (λx. eval_fds f (g x))"
by (rule continuous_within_compose3[OF _ assms(1)] continuous_intros assms)+
lemma continuous_on_eval_fds [continuous_intros]:
fixes f :: "'a :: dirichlet_series fds"
assumes "A ⊆ {s. s ∙ 1 > conv_abscissa f}"
shows "continuous_on A (eval_fds f)"
by (rule DERIV_continuous_on derivative_intros)+ (insert assms, auto)
lemma continuous_on_eval_fds' [continuous_intros]:
fixes f :: "'a :: dirichlet_series fds"
assumes "continuous_on A g" "g ` A ⊆ {s. s ∙ 1 > conv_abscissa f}"
shows "continuous_on A (λx. eval_fds f (g x))"
by (rule continuous_on_compose2[OF continuous_on_eval_fds assms(1)])
(insert assms, auto simp: image_iff)
lemma conv_abscissa_deriv_le:
fixes f :: "'a fds"
shows "conv_abscissa (fds_deriv f) ≤ conv_abscissa f"
proof (rule conv_abscissa_leI)
fix c' :: real
assume "ereal c' > conv_abscissa f"
thus "∃s. s ∙ 1 = c' ∧ fds_converges (fds_deriv f) s"
by (intro exI[of _ "of_real c'"]) (auto simp: fds_converges_deriv)
qed
lemma abs_conv_abscissa_integral:
fixes f :: "'a fds"
shows "abs_conv_abscissa (fds_integral a f) = abs_conv_abscissa f"
proof (rule antisym)
show "abs_conv_abscissa (fds_integral a f) ≤ abs_conv_abscissa f"
proof (rule abs_conv_abscissa_leI, goal_cases)
case (1 c)
have "fds_abs_converges (fds_integral a f) (of_real c)"
unfolding fds_abs_converges_def
proof (rule summable_comparison_test_ev)
from 1 have "fds_abs_converges f (of_real c)"
by (intro fds_abs_converges) auto
thus "summable (λn. norm (fds_nth f n / nat_power n (of_real c)))"
by (simp add: fds_abs_converges_def)
next
show "∀⇩F n in sequentially. norm (norm (fds_nth (fds_integral a f) n / nat_power n (of_real c))) ≤
norm (fds_nth f n / nat_power n (of_real c))"
using eventually_gt_at_top[of 3]
proof eventually_elim
case (elim n)
from elim and exp_le have "ln (exp 1) ≤ ln (real n)"
by (subst ln_le_cancel_iff) auto
hence "1 * norm (fds_nth f n) ≤ ln (real n) * norm (fds_nth f n)"
by (intro mult_right_mono) auto
with elim show ?case
by (simp add: norm_divide norm_nat_power fds_integral_def field_simps)
qed
qed
thus ?case by (intro exI[of _ "of_real c"]) auto
qed
next
show "abs_conv_abscissa f ≤ abs_conv_abscissa (fds_integral a f)" (is "_ ≤ ?s0")
proof (cases "abs_conv_abscissa (fds_integral a f) = ∞")
case False
show ?thesis
proof (rule abs_conv_abscissa_leI)
fix c :: real
define ε where "ε = (if ?s0 = -∞ then 1 else (c - real_of_ereal ?s0) / 2)"
assume "ereal c > ?s0"
with False have ε: "ε > 0" "c - ε > ?s0"
by (cases ?s0; force simp: ε_def field_simps)+
have "fds_abs_converges f (of_real c)"
unfolding fds_abs_converges_def
proof (rule summable_comparison_test_ev)
from ε have "fds_abs_converges (fds_integral a f) (of_real (c - ε))"
by (intro fds_abs_converges) (auto simp: algebra_simps)
thus "summable (λn. norm (fds_nth (fds_integral a f) n / nat_power n (of_real (c - ε))))"
by (simp add: fds_abs_converges_def)
next
have "∀⇩F n in at_top. ln (real n) / real n powr ε < 1"
by (rule order_tendstoD lim_ln_over_power ‹ε > 0› zero_less_one)+
thus "∀⇩F n in sequentially. norm (norm (fds_nth f n / nat_power n (of_real c)))
≤ norm (fds_nth (fds_integral a f) n / nat_power n (of_real (c - ε)))"
using eventually_gt_at_top[of 1]
proof eventually_elim
case (elim n)
hence "ln (real n) * norm (fds_nth f n) ≤ real n powr ε * norm (fds_nth f n)"
by (intro mult_right_mono) auto
with elim show ?case
by (simp add: norm_divide norm_nat_power field_simps
powr_diff inner_diff_left fds_integral_def)
qed
qed
thus "∃s. s ∙ 1 = c ∧ fds_abs_converges f s"
by (intro exI[of _ "of_real c"]) auto
qed
qed auto
qed
lemma abs_conv_abscissa_ln:
"abs_conv_abscissa (fds_ln l (f :: 'a :: dirichlet_series fds)) =
abs_conv_abscissa (fds_deriv f / f)"
by (simp add: fds_ln_def abs_conv_abscissa_integral)
lemma abs_conv_abscissa_deriv:
fixes f :: "'a fds"
shows "abs_conv_abscissa (fds_deriv f) = abs_conv_abscissa f"
proof -
have "abs_conv_abscissa (fds_deriv f) =
abs_conv_abscissa (fds_integral (fds_nth f 1) (fds_deriv f))"
by (rule abs_conv_abscissa_integral [symmetric])
also have "fds_integral (fds_nth f 1) (fds_deriv f) = f"
by (rule fds_integral_fds_deriv)
finally show ?thesis .
qed
lemma abs_conv_abscissa_higher_deriv:
"abs_conv_abscissa ((fds_deriv ^^ n) f) = abs_conv_abscissa (f :: 'a :: dirichlet_series fds)"
by (induction n) (simp_all add: abs_conv_abscissa_deriv)
lemma conv_abscissa_higher_deriv_le:
"conv_abscissa ((fds_deriv ^^ n) f) ≤ conv_abscissa (f :: 'a :: dirichlet_series fds)"
by (induction n) (auto intro: order.trans[OF conv_abscissa_deriv_le])
lemma abs_conv_abscissa_restrict:
"abs_conv_abscissa (fds_subseries P f) ≤ abs_conv_abscissa f"
by (rule abs_conv_abscissa_mono) auto
lemma eval_fds_deriv:
fixes f :: "'a fds"
assumes "s ∙ 1 > conv_abscissa f"
shows "eval_fds (fds_deriv f) s = deriv (eval_fds f) s"
by (intro DERIV_imp_deriv [symmetric] derivative_intros assms)
lemma eval_fds_higher_deriv:
assumes "(s :: 'a :: dirichlet_series) ∙ 1 > conv_abscissa f"
shows "eval_fds ((fds_deriv ^^ n) f) s = (deriv ^^ n) (eval_fds f) s"
using assms
proof (induction n arbitrary: f s)
case (Suc n f s)
have ev: "eventually (λs. s ∈ {s. s ∙ 1 > conv_abscissa f}) (nhds s)"
using Suc.prems open_halfspace_gt[of _ "1::'a"]
by (intro eventually_nhds_in_open, cases "conv_abscissa f")
(auto simp: open_halfspace_gt inner_commute)
have "eval_fds ((fds_deriv ^^ Suc n) f) s = eval_fds ((fds_deriv ^^ n) (fds_deriv f)) s"
by (subst funpow_Suc_right) simp
also have "… = (deriv ^^ n) (eval_fds (fds_deriv f)) s"
by (intro Suc.IH le_less_trans[OF conv_abscissa_deriv_le] Suc.prems)
also have "… = (deriv ^^ n) (deriv (eval_fds f)) s"
by (intro higher_deriv_cong_ev refl eventually_mono[OF ev] eval_fds_deriv) auto
also have "… = (deriv ^^ Suc n) (eval_fds f) s"
by (subst funpow_Suc_right) simp
finally show ?case .
qed auto
end
subsection ‹Multiplication of two series›
lemma
fixes f g :: "nat ⇒ 'a :: {banach, real_normed_field, second_countable_topology, nat_power}"
fixes s :: 'a
assumes [simp]: "f 0 = 0" "g 0 = 0"
assumes summable: "summable (λn. norm (f n / nat_power n s))"
"summable (λn. norm (g n / nat_power n s))"
shows summable_dirichlet_prod: "summable (λn. norm (dirichlet_prod f g n / nat_power n s))"
and suminf_dirichlet_prod:
"(∑n. dirichlet_prod f g n / nat_power n s) =
(∑n. f n / nat_power n s) * (∑n. g n / nat_power n s)"
proof -
have summable': "(λn. f n / nat_power n s) abs_summable_on A"
"(λn. g n / nat_power n s) abs_summable_on A" for A
by ((rule abs_summable_on_subset[OF _ subset_UNIV], insert summable,
simp add: abs_summable_on_nat_iff'); fail)+
have f_g: "f a / nat_power a s * (g b / nat_power b s) =
f a * g b / nat_power (a * b) s" for a b
by (cases "a * b = 0") (auto simp: nat_power_mult_distrib)
have eq: "(∑⇩a(m, n)∈{(m, n). m * n = x}. f m * g n / nat_power x s) =
dirichlet_prod f g x / nat_power x s" for x :: nat
proof (cases "x > 0")
case False
hence "(∑⇩a(m,n) | m * n = x. f m * g n / nat_power x s) = (∑⇩a(m,n) | m * n = x. 0)"
by (intro infsetsum_cong) auto
with False show ?thesis by simp
next
case True
from finite_divisors_nat'[OF this] show ?thesis
by (simp add: dirichlet_prod_altdef2 case_prod_unfold sum_divide_distrib)
qed
have "(λ(m,n). (f m / nat_power m s) * (g n / nat_power n s)) abs_summable_on UNIV × UNIV"
using summable' by (intro abs_summable_on_product) auto
also have "?this ⟷ (λ(m,n). f m * g n / nat_power (m*n) s) abs_summable_on UNIV"
using f_g by (intro abs_summable_on_cong) auto
also have "… ⟷ (λ(x,(m,n)). f m * g n / nat_power (m*n) s) abs_summable_on
(SIGMA x:UNIV. {(m,n). m * n = x})"
unfolding case_prod_unfold
by (rule abs_summable_on_reindex_bij_betw [symmetric])
(auto simp: bij_betw_def inj_on_def image_iff)
also have "… ⟷ (λ(x,(m,n)). f m * g n / nat_power x s) abs_summable_on
(SIGMA x:UNIV. {(m,n). m * n = x})"
by (intro abs_summable_on_cong) auto
finally have summable'': … .
from abs_summable_on_Sigma_project1'[OF this]
show summable''': "summable (λn. norm (dirichlet_prod f g n / nat_power n s))"
by (simp add: eq abs_summable_on_nat_iff')
have "(∑n. f n / nat_power n s) * (∑n. g n / nat_power n s) =
(∑⇩an. f n / nat_power n s) * (∑⇩an. g n / nat_power n s)"
using summable' by (simp add: infsetsum_nat')
also have "… = (∑⇩a(m,n). (f m / nat_power m s) * (g n / nat_power n s))"
using summable' by (subst infsetsum_product [symmetric]) simp_all
also have "… = (∑⇩a(m,n). f m * g n / nat_power (m * n) s)"
using f_g by (intro infsetsum_cong refl) auto
also have "… = (∑⇩a(x,(m,n))∈(SIGMA x:UNIV. {(m,n). m * n = x}).
f m * g n / nat_power (m * n) s)"
unfolding case_prod_unfold
by (rule infsetsum_reindex_bij_betw [symmetric]) (auto simp: bij_betw_def inj_on_def image_iff)
also have "… = (∑⇩a(x,(m,n))∈(SIGMA x:UNIV. {(m,n). m * n = x}).
f m * g n / nat_power x s)"
by (intro infsetsum_cong refl) (auto simp: case_prod_unfold)
also have "… = (∑⇩ax. dirichlet_prod f g x / nat_power x s)"
(is "_ = infsetsum ?T _") using summable'' by (subst infsetsum_Sigma) (auto simp: eq)
also have "… = (∑x. dirichlet_prod f g x / nat_power x s)"
using summable''' by (intro infsetsum_nat') (simp_all add: abs_summable_on_nat_iff')
finally show "… = (∑n. f n / nat_power n s) * (∑n. g n / nat_power n s)" ..
qed
lemma
fixes f g :: "nat ⇒ real"
fixes s :: real
assumes "f 0 = 0" "g 0 = 0"
assumes summable: "summable (λn. norm (f n / real n powr s))"
"summable (λn. norm (g n / real n powr s))"
shows summable_dirichlet_prod_real: "summable (λn. norm (dirichlet_prod f g n / real n powr s))"
and suminf_dirichlet_prod_real:
"(∑n. dirichlet_prod f g n / real n powr s) =
(∑n. f n / nat_power n s) * (∑n. g n / real n powr s)"
using summable_dirichlet_prod[of f g s] suminf_dirichlet_prod[of f g s] assms by simp_all
lemma fds_abs_converges_mult:
fixes s :: "'a :: {nat_power, real_normed_field, banach, second_countable_topology}"
assumes "fds_abs_converges f s" "fds_abs_converges g s"
shows "fds_abs_converges (f * g) s"
using summable_dirichlet_prod[OF _ _ assms[unfolded fds_abs_converges_def]]
by (simp add: fds_abs_converges_def fds_nth_mult)
lemma fds_abs_converges_power:
fixes s :: "'a :: {nat_power, real_normed_field, banach, second_countable_topology}"
shows "fds_abs_converges f s ⟹ fds_abs_converges (f ^ n) s"
by (induction n) (auto intro!: fds_abs_converges_mult)
lemma fds_abs_converges_prod:
fixes s :: "'a :: {nat_power, real_normed_field, banach, second_countable_topology}"
shows "(⋀x. x ∈ A ⟹ fds_abs_converges (f x) s) ⟹ fds_abs_converges (prod f A) s"
by (induction A rule: infinite_finite_induct) (auto intro!: fds_abs_converges_mult)
lemma abs_conv_abscissa_mult_le:
"abs_conv_abscissa (f * g :: 'a :: dirichlet_series fds) ≤
max (abs_conv_abscissa f) (abs_conv_abscissa g)"
proof (rule abs_conv_abscissa_leI, goal_cases)
case (1 c')
thus ?case
by (auto intro!: exI[of _ "of_real c'"] fds_abs_converges_mult intro: fds_abs_converges)
qed
lemma abs_conv_abscissa_mult_leI:
"abs_conv_abscissa (f :: 'a :: dirichlet_series fds) ≤ d ⟹
abs_conv_abscissa g ≤ d ⟹ abs_conv_abscissa (f * g) ≤ d"
using abs_conv_abscissa_mult_le[of f g] by (auto simp add: le_max_iff_disj)
lemma abs_conv_abscissa_shift [simp]:
"abs_conv_abscissa (fds_shift c f) = abs_conv_abscissa (f :: 'a :: dirichlet_series fds) + c ∙ 1"
proof -
have "abs_conv_abscissa (fds_shift c f) ≤ abs_conv_abscissa f + c ∙ 1" for c :: 'a and f
proof (rule abs_conv_abscissa_leI)
fix d assume "abs_conv_abscissa f + c ∙ 1 < ereal d"
hence "abs_conv_abscissa f < ereal (d - c ∙ 1)" by (cases "abs_conv_abscissa f") auto
hence "fds_abs_converges (fds_shift c f) (of_real d)"
by (auto intro!: fds_abs_converges_shift fds_abs_converges simp: algebra_simps)
thus "∃s. s ∙ 1 = d ∧ fds_abs_converges (fds_shift c f) s"
by (auto intro!: exI[of _ "of_real d"])
qed
note * = this[of c f] this[of "-c" "fds_shift c f"]
show ?thesis by (cases "abs_conv_abscissa (fds_shift c f)"; cases "abs_conv_abscissa f")
(insert *, auto intro!: antisym)
qed
lemma eval_fds_mult:
fixes s :: "'a :: {nat_power, real_normed_field, banach, second_countable_topology}"
assumes "fds_abs_converges f s" "fds_abs_converges g s"
shows "eval_fds (f * g) s = eval_fds f s * eval_fds g s"
using suminf_dirichlet_prod[OF _ _ assms[unfolded fds_abs_converges_def]]
by (simp_all add: eval_fds_def fds_nth_mult)
lemma eval_fds_power:
fixes s :: "'a :: {nat_power, real_normed_field, banach, second_countable_topology}"
assumes "fds_abs_converges f s"
shows "eval_fds (f ^ n) s = eval_fds f s ^ n"
using assms by (induction n) (simp_all add: eval_fds_mult fds_abs_converges_power)
lemma eval_fds_prod:
fixes s :: "'a :: {nat_power, real_normed_field, banach, second_countable_topology}"
assumes "(⋀x. x ∈ A ⟹ fds_abs_converges (f x) s)"
shows "eval_fds (prod f A) s = (∏x∈A. eval_fds (f x) s)" using assms
by (induction A rule: infinite_finite_induct) (auto simp: eval_fds_mult fds_abs_converges_prod)
lemma eval_fds_inverse:
fixes s :: "'a :: {nat_power, real_normed_field, banach, second_countable_topology}"
assumes "fds_abs_converges f s" "fds_abs_converges (inverse f) s" "fds_nth f 1 ≠ 0"
shows "eval_fds (inverse f) s = inverse (eval_fds f s)"
proof -
have "eval_fds (inverse f * f) s = eval_fds (inverse f) s * eval_fds f s"
by (intro eval_fds_mult assms)
also have "inverse f * f = 1" by (intro fds_left_inverse assms)
also have "eval_fds 1 s = 1" by simp
finally show ?thesis by (auto simp: divide_simps)
qed
lemma eval_fds_integral_has_field_derivative:
fixes s :: "'a :: dirichlet_series"
assumes "ereal (s ∙ 1) > abs_conv_abscissa f"
assumes "fds_nth f 1 = 0"
shows "(eval_fds (fds_integral c f) has_field_derivative eval_fds f s) (at s)"
proof -
have "conv_abscissa (fds_integral c f) ≤ abs_conv_abscissa (fds_integral c f)"
by (rule conv_le_abs_conv_abscissa)
also from assms have "… < ereal (s ∙ 1)" by (simp add: abs_conv_abscissa_integral)
finally have "(eval_fds (fds_integral c f) has_field_derivative
eval_fds (fds_deriv (fds_integral c f)) s) (at s)"
by (intro derivative_eq_intros) auto
also from assms have "fds_deriv (fds_integral c f) = f"
by simp
finally show ?thesis .
qed
lemma holomorphic_fds_eval [holomorphic_intros]:
"A ⊆ {z. Re z > conv_abscissa f} ⟹ eval_fds f holomorphic_on A"
unfolding holomorphic_on_def field_differentiable_def
by (rule ballI exI derivative_intros)+ auto
lemma analytic_fds_eval [holomorphic_intros]:
assumes "A ⊆ {z. Re z > conv_abscissa f}"
shows "eval_fds f analytic_on A"
proof -
have "eval_fds f analytic_on {z. Re z > conv_abscissa f}"
proof (subst analytic_on_open)
show "open {z. Re z > conv_abscissa f}"
by (cases "conv_abscissa f") (simp_all add: open_halfspace_Re_gt)
qed (intro holomorphic_intros, simp_all)
from analytic_on_subset[OF this assms] show ?thesis .
qed
lemma conv_abscissa_0 [simp]:
"conv_abscissa (0 :: 'a :: dirichlet_series fds) = -∞"
by (auto simp: conv_abscissa_MInf_iff)
lemma abs_conv_abscissa_0 [simp]:
"abs_conv_abscissa (0 :: 'a :: dirichlet_series fds) = -∞"
by (auto simp: abs_conv_abscissa_MInf_iff)
lemma conv_abscissa_1 [simp]:
"conv_abscissa (1 :: 'a :: dirichlet_series fds) = -∞"
by (auto simp: conv_abscissa_MInf_iff)
lemma abs_conv_abscissa_1 [simp]:
"abs_conv_abscissa (1 :: 'a :: dirichlet_series fds) = -∞"
by (auto simp: abs_conv_abscissa_MInf_iff)
lemma conv_abscissa_const [simp]:
"conv_abscissa (fds_const (c :: 'a :: dirichlet_series)) = -∞"
by (auto simp: conv_abscissa_MInf_iff)
lemma abs_conv_abscissa_const [simp]:
"abs_conv_abscissa (fds_const (c :: 'a :: dirichlet_series)) = -∞"
by (auto simp: abs_conv_abscissa_MInf_iff)
lemma conv_abscissa_numeral [simp]:
"conv_abscissa (numeral n :: 'a :: dirichlet_series fds) = -∞"
by (auto simp: numeral_fds)
lemma abs_conv_abscissa_numeral [simp]:
"abs_conv_abscissa (numeral n :: 'a :: dirichlet_series fds) = -∞"
by (auto simp: numeral_fds)
lemma abs_conv_abscissa_power_le:
"abs_conv_abscissa (f ^ n :: 'a :: dirichlet_series fds) ≤ abs_conv_abscissa f"
by (induction n) (auto intro!: order.trans[OF abs_conv_abscissa_mult_le])
lemma abs_conv_abscissa_power_leI:
"abs_conv_abscissa (f :: 'a :: dirichlet_series fds) ≤ d ⟹ abs_conv_abscissa (f ^ n) ≤ d"
by (rule order.trans[OF abs_conv_abscissa_power_le])
lemma abs_conv_abscissa_prod_le:
assumes "⋀x. x ∈ A ⟹ abs_conv_abscissa (f x :: 'a :: dirichlet_series fds) ≤ d"
shows "abs_conv_abscissa (prod f A) ≤ d" using assms
by (induction A rule: infinite_finite_induct) (auto intro!: abs_conv_abscissa_mult_leI)
lemma conv_abscissa_add_le:
"conv_abscissa (f + g :: 'a :: dirichlet_series fds) ≤ max (conv_abscissa f) (conv_abscissa g)"
by (rule conv_abscissa_leI_weak) (auto intro!: fds_converges_add intro: fds_converges)
lemma conv_abscissa_add_leI:
"conv_abscissa (f :: 'a :: dirichlet_series fds) ≤ d ⟹ conv_abscissa g ≤ d ⟹
conv_abscissa (f + g) ≤ d"
using conv_abscissa_add_le[of f g] by (auto simp: le_max_iff_disj)
lemma conv_abscissa_sum_leI:
assumes "⋀x. x ∈ A ⟹ conv_abscissa (f x :: 'a :: dirichlet_series fds) ≤ d"
shows "conv_abscissa (sum f A) ≤ d" using assms
by (induction A rule: infinite_finite_induct) (auto intro!: conv_abscissa_add_leI)
lemma abs_conv_abscissa_add_le:
"abs_conv_abscissa (f + g :: 'a :: dirichlet_series fds) ≤ max (abs_conv_abscissa f) (abs_conv_abscissa g)"
by (rule abs_conv_abscissa_leI_weak) (auto intro!: fds_abs_converges_add intro: fds_abs_converges)
lemma abs_conv_abscissa_add_leI:
"abs_conv_abscissa (f :: 'a :: dirichlet_series fds) ≤ d ⟹ abs_conv_abscissa g ≤ d ⟹
abs_conv_abscissa (f + g) ≤ d"
using abs_conv_abscissa_add_le[of f g] by (auto simp: le_max_iff_disj)
lemma abs_conv_abscissa_sum_leI:
assumes "⋀x. x ∈ A ⟹ abs_conv_abscissa (f x :: 'a :: dirichlet_series fds) ≤ d"
shows "abs_conv_abscissa (sum f A) ≤ d" using assms
by (induction A rule: infinite_finite_induct) (auto intro!: abs_conv_abscissa_add_leI)
lemma fds_converges_cmult_left [intro]:
assumes "fds_converges f s"
shows "fds_converges (fds_const c * f) s"
proof -
from assms have "summable (λn. c * (fds_nth f n / nat_power n s))"
by (intro summable_mult) (auto simp: fds_converges_def)
thus ?thesis by (simp add: fds_converges_def mult_ac)
qed
lemma fds_converges_cmult_right [intro]:
assumes "fds_converges f s"
shows "fds_converges (f * fds_const c) s"
using fds_converges_cmult_left[OF assms] by (simp add: mult_ac)
lemma conv_abscissa_cmult_left [simp]:
fixes c :: "'a :: dirichlet_series" assumes "c ≠ 0"
shows "conv_abscissa (fds_const c * f) = conv_abscissa f"
proof -
have "fds_converges (fds_const c * f) s ⟷ fds_converges f s" for s
proof
assume "fds_converges (fds_const c * f) s"
hence "fds_converges (fds_const (inverse c) * (fds_const c * f)) s"
by (rule fds_converges_cmult_left)
also have "fds_const (inverse c) * (fds_const c * f) = fds_const (inverse c * c) * f"
by simp
also have "inverse c * c = 1"
using assms by simp
finally show "fds_converges f s" by simp
qed auto
thus ?thesis by (simp add: conv_abscissa_def)
qed
lemma conv_abscissa_cmult_right [simp]:
fixes c :: "'a :: dirichlet_series" assumes "c ≠ 0"
shows "conv_abscissa (f * fds_const c) = conv_abscissa f"
using assms by (subst mult.commute) auto
lemma abs_conv_abscissa_cmult:
fixes c :: "'a :: dirichlet_series" assumes "c ≠ 0"
shows "abs_conv_abscissa (fds_const c * f) = abs_conv_abscissa f"
proof (intro antisym)
have "abs_conv_abscissa (fds_const (inverse c) * (fds_const c * f)) ≤
abs_conv_abscissa (fds_const c * f)"
using abs_conv_abscissa_mult_le[of "fds_const (inverse c)" "fds_const c * f"]
by (auto simp: max_def)
also have "fds_const (inverse c) * (fds_const c * f) = fds_const (inverse c * c) * f"
by (simp add: mult_ac)
also have "inverse c * c = 1" using assms by simp
finally show "abs_conv_abscissa f ≤ abs_conv_abscissa (fds_const c * f)" by simp
qed (insert abs_conv_abscissa_mult_le[of "fds_const c" f], auto simp: max_def)
lemma conv_abscissa_minus [simp]:
fixes f :: "'a :: dirichlet_series fds"
shows "conv_abscissa (-f) = conv_abscissa f"
using conv_abscissa_cmult_left[of "-1" f] by simp
lemma abs_conv_abscissa_minus [simp]:
fixes f :: "'a :: dirichlet_series fds"
shows "abs_conv_abscissa (-f) = abs_conv_abscissa f"
using abs_conv_abscissa_cmult[of "-1" f] by simp
lemma conv_abscissa_diff_le:
"conv_abscissa (f - g :: 'a :: dirichlet_series fds) ≤ max (conv_abscissa f) (conv_abscissa g)"
using conv_abscissa_add_le[of f "-g"] by simp
lemma conv_abscissa_diff_leI:
"conv_abscissa (f :: 'a :: dirichlet_series fds) ≤ d ⟹ conv_abscissa g ≤ d ⟹
conv_abscissa (f - g) ≤ d"
using conv_abscissa_add_le[of f "-g"] by (auto simp: le_max_iff_disj)
lemma abs_conv_abscissa_diff_le:
"abs_conv_abscissa (f - g :: 'a :: dirichlet_series fds) ≤
max (abs_conv_abscissa f) (abs_conv_abscissa g)"
using abs_conv_abscissa_add_le[of f "-g"] by simp
lemma abs_conv_abscissa_diff_leI:
"abs_conv_abscissa (f :: 'a :: dirichlet_series fds) ≤ d ⟹ abs_conv_abscissa g ≤ d ⟹
abs_conv_abscissa (f - g) ≤ d"
using abs_conv_abscissa_add_le[of f "-g"] by (auto simp: le_max_iff_disj)
lemmas eval_fds_integral_has_field_derivative' [derivative_intros] =
DERIV_chain'[OF _ eval_fds_integral_has_field_derivative]
lemma abs_conv_abscissa_completely_multiplicative_log_deriv:
fixes f :: "'a :: dirichlet_series fds"
assumes "completely_multiplicative_function (fds_nth f)" "fds_nth f 1 ≠ 0"
shows "abs_conv_abscissa (fds_deriv f / f) ≤ abs_conv_abscissa f"
proof -
have "fds_deriv f = - fds (λn. fds_nth f n * mangoldt n) * f"
using assms by (subst completely_multiplicative_fds_deriv') simp_all
also have "… / f = - fds (λn. fds_nth f n * mangoldt n) * (f * inverse f)"
by (simp add: divide_fds_def)
also have "f * inverse f = 1" using assms by (intro fds_right_inverse)
finally have "fds_deriv f / f = - fds (λn. fds_nth f n * mangoldt n)" by simp
also have "abs_conv_abscissa … =
abs_conv_abscissa (fds (λn. fds_nth f n * mangoldt n))"
(is "_ = abs_conv_abscissa ?f") by (rule abs_conv_abscissa_minus)
also have "… ≤ abs_conv_abscissa f"
proof (rule abs_conv_abscissa_leI, goal_cases)
case (1 c)
have "fds_abs_converges ?f (of_real c)" unfolding fds_abs_converges_def
proof (rule summable_comparison_test_ev)
from 1 have "fds_abs_converges (fds_deriv f) (of_real c)"
by (intro fds_abs_converges) (auto simp: abs_conv_abscissa_deriv)
thus "summable (λn. ¦ln (real n)¦ * norm (fds_nth f n) / norm (nat_power n (of_real c :: 'a)))"
by (simp add: fds_abs_converges_def fds_deriv_def fds_nth_fds'
scaleR_conv_of_real powr_minus norm_mult norm_divide norm_nat_power)
next
show "∀⇩F n in sequentially.
norm (norm (fds_nth (fds (λn. fds_nth f n * mangoldt n)) n /
nat_power n (of_real c)))
≤ ¦ln (real n)¦ * norm (fds_nth f n) / norm (nat_power n (of_real c) :: 'a)"
using eventually_gt_at_top[of 0]
proof eventually_elim
case (elim n)
have "norm (norm (fds_nth (fds (λn. fds_nth f n * mangoldt n)) n /
nat_power n (of_real c))) =
norm (fds_nth f n) * mangoldt n / real n powr c"
using elim by (simp add: fds_nth_fds' norm_mult norm_divide
norm_nat_power abs_mult mangoldt_nonneg)
also have "… ≤ norm (fds_nth f n) * ln n / real n powr c" using elim
by (intro mult_left_mono divide_right_mono mangoldt_le)
(simp_all add: mangoldt_def)
finally show ?case using elim by (simp add: norm_nat_power algebra_simps)
qed
qed
thus ?case by (intro exI[of _ "of_real c"]) auto
qed
finally show ?thesis .
qed
subsection ‹Uniqueness›
context
assumes "SORT_CONSTRAINT ('a :: dirichlet_series)"
begin
lemma norm_dirichlet_series_cutoff_le:
assumes "fds_abs_converges f (s0 :: 'a)" "N > 0" "s ∙ 1 ≥ c" "c ≥ s0 ∙ 1"
shows "summable (λn. fds_nth f (n + N) / nat_power (n + N) s)"
"summable (λn. norm (fds_nth f (n + N)) / nat_power (n + N) c)"
and "norm (∑n. fds_nth f (n + N) / nat_power (n + N) s) ≤
(∑n. norm (fds_nth f (n + N)) / nat_power (n + N) c) / nat_power N (s ∙ 1 - c)"
proof -
from assms have "fds_abs_converges f (of_real c)"
using fds_abs_converges_Re_le[of f s0 "of_real c"] by auto
hence "summable (λn. norm (fds_nth f (n + N) / nat_power (n + N) (of_real c)))"
unfolding fds_abs_converges_def by (rule summable_ignore_initial_segment)
also have "?this ⟷ summable (λn. norm (fds_nth f (n + N)) / nat_power (n + N) c)"
by (intro summable_cong eventually_mono[OF eventually_gt_at_top[of "0::nat"]])
(auto simp: norm_divide norm_nat_power)
finally show *: "summable (λn. norm (fds_nth f (n + N)) / nat_power (n + N) c)" .
from assms have "fds_abs_converges f s" using fds_abs_converges_Re_le[of f s0 s] by auto
hence **: "summable (λn. norm (fds_nth f (n + N) / nat_power (n + N) s))"
unfolding fds_abs_converges_def by (rule summable_ignore_initial_segment)
thus "summable (λn. fds_nth f (n + N) / nat_power (n + N) s)"
by (rule summable_norm_cancel)
have "norm (∑n. fds_nth f (n + N) / nat_power (n + N) s)
≤ (∑n. norm (fds_nth f (n + N) / nat_power (n + N) s))"
by (intro summable_norm **)
also have "… ≤ (∑n. norm (fds_nth f (n + N)) / nat_power (n + N) c / nat_power N (s ∙ 1 - c))"
proof (intro suminf_le * ** summable_divide allI)
fix n :: nat
have "real N powr (s ∙ 1 - c) ≤ real (n + N) powr (s ∙ 1 - c)"
using assms by (intro powr_mono2) simp_all
also have "real (n + N) powr c * … = real (n + N) powr (s ∙ 1)"
by (simp add: powr_diff)
finally have "norm (fds_nth f (n + N)) / real (n + N) powr (s ∙ 1) ≤
norm (fds_nth f (n + N)) / (real (n + N) powr c * real N powr (s ∙ 1 - c))"
using ‹N > 0› by (intro divide_left_mono) (simp_all add: mult_left_mono)
thus "norm (fds_nth f (n + N) / nat_power (n + N) s) ≤
norm (fds_nth f (n + N)) / nat_power (n + N) c / nat_power N (s ∙ 1 - c)"
using ‹N > 0› by (simp add: norm_divide norm_nat_power )
qed
also have "… = (∑n. norm (fds_nth f (n + N)) / nat_power (n + N) c) / nat_power N (s ∙ 1 - c)"
using * by (rule suminf_divide)
finally show "norm (∑n. fds_nth f (n + N) / nat_power (n + N) s) ≤ …" .
qed
lemma eval_fds_zeroD_aux:
fixes h :: "'a fds"
assumes conv: "fds_abs_converges h (s0 :: 'a)"
assumes freq: "frequently (λs. eval_fds h s = 0) ((λs. s ∙ 1) going_to at_top)"
shows "h = 0"
proof (rule ccontr)
assume "h ≠ 0"
hence ex: "∃n>0. fds_nth h n ≠ 0" by (auto simp: fds_eq_iff)
define N :: nat where "N = (LEAST n. n > 0 ∧ fds_nth h n ≠ 0)"
have N: "N > 0" "fds_nth h N ≠ 0"
using LeastI_ex[OF ex, folded N_def] by auto
have less_N: "fds_nth h n = 0" if "n < N" for n
using Least_le[of "λn. n > 0 ∧ fds_nth h n ≠ 0" n, folded N_def] that
by (cases "n = 0") (auto simp: not_less)
define c where "c = s0 ∙ 1"
define remainder where "remainder = (λs. (∑n. fds_nth h (n + Suc N) / nat_power (n + Suc N) s))"
define A where "A = (∑n. norm (fds_nth h (n + Suc N)) / nat_power (n + Suc N) c) *
nat_power (Suc N) c"
have eq: "fds_nth h N = nat_power N s * eval_fds h s - nat_power N s * remainder s"
if "s ∙ 1 ≥ c" for s :: 'a
proof -
from conv and that have conv': "fds_abs_converges h s"
unfolding c_def by (rule fds_abs_converges_Re_le)
hence conv'': "fds_converges h s" by blast
from conv'' have "(λn. fds_nth h n / nat_power n s) sums eval_fds h s"
by (simp add: fds_converges_iff)
hence "(λn. fds_nth h (n + Suc N) / nat_power (n + Suc N) s) sums
(eval_fds h s - (∑n<Suc N. fds_nth h n / nat_power n s))"
by (rule sums_split_initial_segment)
also have "(∑n<Suc N. fds_nth h n / nat_power n s) =
(∑n<Suc N. if n = N then fds_nth h N / nat_power N s else 0)"
by (intro sum.cong refl) (auto simp: less_N)
also have "… = fds_nth h N / nat_power N s" by (subst sum.delta) auto
finally show ?thesis unfolding remainder_def using ‹N > 0› by (auto simp: sums_iff field_simps)
qed
have remainder_bound: "norm (remainder s) ≤ A / real (Suc N) powr (s ∙ 1)"
if "s ∙ 1 ≥ c" for s :: 'a
proof -
note * = norm_dirichlet_series_cutoff_le[of h s0 "Suc N" c s, folded remainder_def]
have "norm (remainder s) ≤ (∑n. norm (fds_nth h (n + Suc N)) /
nat_power (n + Suc N) c) / nat_power (Suc N) (s ∙ 1 - c)"
using that assms unfolding remainder_def by (intro *) (simp_all add: c_def)
also have "… = A / real (Suc N) powr (s ∙ 1)" by (simp add: A_def powr_diff)
finally show ?thesis .
qed
from freq have "∀c. ∃s. s ∙ 1 ≥ c ∧ eval_fds h s = 0"
unfolding frequently_def by (auto simp: eventually_going_to_at_top_linorder)
hence "∀k. ∃s. s ∙ 1 ≥ real k ∧ eval_fds h s = 0" by blast
then obtain S where S: "⋀k. S k ∙ 1 ≥ real k ∧ eval_fds h (S k) = 0"
by metis
have S_limit: "filterlim (λk. S k ∙ 1) at_top sequentially"
by (rule filterlim_at_top_mono[OF filterlim_real_sequentially]) (use S in auto)
have "eventually (λk. real k ≥ c) sequentially" by real_asymp
hence "eventually (λk. norm (fds_nth h N) ≤
(real N / real (Suc N)) powr (S k ∙ 1) * A) sequentially"
proof eventually_elim
case (elim k)
hence "norm (fds_nth h N) = real N powr (S k ∙ 1) * norm (remainder (S k))"
(is "_ = _ * ?X") using ‹N > 0› S[of k] eq[of "S k"]
by (auto simp: norm_mult norm_nat_power c_def)
also have "norm (remainder (S k)) ≤ A / real (Suc N) powr (S k ∙ 1)"
using elim S[of k] by (intro remainder_bound) (simp_all add: c_def)
finally show ?case
using N by (simp add: mult_left_mono powr_divide field_simps del: of_nat_Suc)
qed
moreover have "((λk. (real N / real (Suc N)) powr (S k ∙ 1) * A) ⤏ 0) sequentially"
by (rule filterlim_compose[OF _ S_limit]) (use ‹N > 0› in real_asymp)
ultimately have "((λ_. fds_nth h N) ⤏ 0) sequentially"
by (rule Lim_null_comparison)
hence "fds_nth h N = 0" by (simp add: tendsto_const_iff)
with ‹fds_nth h N ≠ 0› show False by contradiction
qed
lemma eval_fds_zeroD:
fixes h :: "'a fds"
assumes conv: "conv_abscissa h < ∞"
assumes freq: "frequently (λs. eval_fds h s = 0) ((λs. s ∙ 1) going_to at_top)"
shows "h = 0"
proof -
have [simp]: "2 ∙ (1 :: 'a) = 2"
using of_real_inner_1[of 2] unfolding of_real_numeral by simp
from conv obtain s where "fds_converges h s"
by auto
hence "fds_abs_converges h (s + 2)"
by (rule fds_converges_imp_abs_converges) (auto simp: algebra_simps)
from this assms(2-) show ?thesis by (rule eval_fds_zeroD_aux)
qed
lemma eval_fds_eqD:
fixes f g :: "'a fds"
assumes conv: "conv_abscissa f < ∞" "conv_abscissa g < ∞"
assumes eq: "frequently (λs. eval_fds f s = eval_fds g s) ((λs. s ∙ 1) going_to at_top)"
shows "f = g"
proof -
have conv': "conv_abscissa (f - g) < ∞"
using assms by (intro le_less_trans[OF conv_abscissa_diff_le]) (auto simp: max_def)
have "max (conv_abscissa f) (conv_abscissa g) < ∞"
using conv by (auto simp: max_def)
from ereal_dense2[OF this] obtain c where c: "max (conv_abscissa f) (conv_abscissa g) < ereal c"
by auto
have "frequently (λs. eval_fds f s = eval_fds g s ∧ s ∙ 1 ≥ c) ((λs. s ∙ 1) going_to at_top)"
using eq by (rule frequently_eventually_frequently) auto
hence *: "frequently (λs. eval_fds (f - g) s = 0) ((λs. s ∙ 1) going_to at_top)"
proof (rule frequently_mono [rotated], safe, goal_cases)
case (1 s)
thus ?case using c
by (subst eval_fds_diff) (auto intro!: fds_converges intro: less_le_trans)
qed
have "f - g = 0" by (rule eval_fds_zeroD fds_abs_converges_diff assms * conv')+
thus ?thesis by simp
qed
end
subsection ‹Limit at infinity›
lemma eval_fds_at_top_tail_bound:
fixes f :: "'a :: dirichlet_series fds"
assumes c: "ereal c > abs_conv_abscissa f"
defines "B ≡ (∑n. norm (fds_nth f (n+2)) / real (n+2) powr c) * 2 powr c"
assumes s: "s ∙ 1 ≥ c"
shows "norm (eval_fds f s - fds_nth f 1) ≤ B / 2 powr (s ∙ 1)"
proof -
from c have "fds_abs_converges f (of_real c)" by (intro fds_abs_converges) simp_all
also have "?this ⟷ summable (λn. norm (fds_nth f n) / real n powr c)"
unfolding fds_abs_converges_def
by (intro summable_cong eventually_mono[OF eventually_gt_at_top[of "0::nat"]])
(auto simp: norm_divide norm_nat_power norm_powr_real_powr)
finally have summable_c: … .
note c
also from s have "ereal c ≤ ereal (s ∙ 1)" by simp
finally have "fds_abs_converges f s" by (intro fds_abs_converges) auto
hence summable: "summable (λn. norm (fds_nth f n / nat_power n s))"
by (simp add: fds_abs_converges_def)
from summable_norm_cancel[OF this]
have "(λn. fds_nth f n / nat_power n s) sums eval_fds f s"
by (simp add: eval_fds_def sums_iff)
from sums_split_initial_segment[OF this, of "Suc (Suc 0)"]
have "norm (eval_fds f s - fds_nth f 1) = norm (∑n. fds_nth f (n+2) / nat_power (n+2) s)"
by (auto simp: sums_iff)
also have "… ≤ (∑n. norm (fds_nth f (n+2) / nat_power (n+2) s))"
by (intro summable_norm summable_ignore_initial_segment summable)
also have "… ≤ (∑n. norm (fds_nth f (n+2)) / real (n+2) powr c / 2 powr (s ∙ 1 - c))"
proof (intro suminf_le allI)
fix n :: nat
have "norm (fds_nth f (n + 2) / nat_power (n + 2) s) =
norm (fds_nth f (n + 2)) / real (n+2) powr c / real (n+2) powr (s ∙ 1 - c)"
by (simp add: field_simps powr_diff norm_divide norm_nat_power)
also have "… ≤ norm (fds_nth f (n + 2)) / real (n+2) powr c / 2 powr (s ∙ 1 - c)" using s
by (intro divide_left_mono divide_nonneg_pos powr_mono2 mult_pos_pos) simp_all
finally show "norm (fds_nth f (n + 2) / nat_power (n + 2) s) ≤ …" .
qed (intro summable_ignore_initial_segment summable summable_divide summable_c)+
also have "… = (∑n. norm (fds_nth f (n+2)) / real (n+2) powr c) / 2 powr (s ∙ 1 - c)"
by (intro suminf_divide summable_ignore_initial_segment summable_c)
also have "… = B / 2 powr (s ∙ 1)" by (simp add: B_def powr_diff)
finally show ?thesis .
qed
lemma tendsto_eval_fds_Re_at_top:
assumes "conv_abscissa (f :: 'a :: dirichlet_series fds) ≠ ∞"
assumes lim: "filterlim (λx. S x ∙ 1) at_top F"
shows "((λx. eval_fds f (S x)) ⤏ fds_nth f 1) F"
proof -
from assms(1) have "abs_conv_abscissa f < ∞"
using abs_conv_le_conv_abscissa_plus_1[of f] by auto
from ereal_dense2[OF this] obtain c where c: "abs_conv_abscissa f < ereal c" by auto
define B where "B = (∑n. norm (fds_nth f (n+2)) / real (n+2) powr c) * 2 powr c"
have *: "norm (eval_fds f s - fds_nth f 1) ≤ B / 2 powr (s ∙ 1)" if s: "s ∙ 1 ≥ c" for s
using eval_fds_at_top_tail_bound[of f c s] that c by (simp add: B_def)
moreover from lim have "eventually (λx. S x ∙ 1 ≥ c) F" by (auto simp: filterlim_at_top)
ultimately have "eventually (λx. norm (eval_fds f (S x) - fds_nth f 1) ≤
B / 2 powr (S x ∙ 1)) F" by (auto elim!: eventually_mono)
moreover have "((λx. B / 2 powr (S x ∙ 1)) ⤏ 0) F"
using filterlim_tendsto_pos_mult_at_top[OF tendsto_const[of "ln 2"] _ lim]
by (intro real_tendsto_divide_at_top[OF tendsto_const])
(auto simp: powr_def mult_ac intro!: filterlim_compose[OF exp_at_top])
ultimately have "((λx. eval_fds f (S x) - fds_nth f 1) ⤏ 0) F"
by (rule Lim_null_comparison)
thus ?thesis by (subst (asm) Lim_null [symmetric])
qed
lemma tendsto_eval_fds_Re_at_top':
assumes "conv_abscissa (f :: complex fds) ≠ ∞"
shows "uniform_limit UNIV (λσ t. eval_fds f (of_real σ + of_real t * 𝗂)
) (λ_ .fds_nth f 1) at_top"
proof -
from assms(1) have "abs_conv_abscissa f < ∞"
using abs_conv_le_conv_abscissa_plus_1[of f] by auto
from ereal_dense2[OF this] obtain c where c: "abs_conv_abscissa f < ereal c" by auto
define B where "B ≡ (∑n. norm (fds_nth f (n+2)) / real (n+2) powr c) * 2 powr c"
show ?thesis
unfolding uniform_limit_iff
proof safe
fix ε :: real assume "ε > 0"
hence "eventually (λσ. B / 2 powr σ < ε) at_top"
by real_asymp
thus "eventually (λσ. ∀t∈UNIV.
dist (eval_fds f (of_real σ + of_real t * 𝗂)) (fds_nth f 1) < ε) at_top"
using eventually_ge_at_top[of c]
proof eventually_elim
case (elim σ)
show ?case
proof
fix t :: real
have "dist (eval_fds f (of_real σ + of_real t * 𝗂)) (fds_nth f 1) ≤ B / 2 powr σ"
using eval_fds_at_top_tail_bound[of f c "of_real σ + of_real t * 𝗂"] elim c
by (simp add: dist_norm B_def)
also have "… < ε" by fact
finally show "dist (eval_fds f (of_real σ + of_real t * 𝗂)) (fds_nth f 1) < ε" .
qed
qed
qed
qed
lemma tendsto_eval_fds_Re_going_to_at_top:
assumes "conv_abscissa (f :: 'a :: dirichlet_series fds) ≠ ∞"
shows "((λs. eval_fds f s) ⤏ fds_nth f 1) ((λs. s ∙ 1) going_to at_top)"
using assms by (rule tendsto_eval_fds_Re_at_top) auto
lemma tendsto_eval_fds_Re_going_to_at_top':
assumes "conv_abscissa (f :: complex fds) ≠ ∞"
shows "((λs. eval_fds f s) ⤏ fds_nth f 1) (Re going_to at_top)"
using assms by (rule tendsto_eval_fds_Re_at_top) auto
text ‹
Any Dirichlet series that is not identically zero and does not diverge everywhere
has a half-plane in which it converges and is non-zero.
›
theorem fds_nonzero_halfplane_exists:
fixes f :: "'a :: dirichlet_series fds"
assumes "conv_abscissa f < ∞" "f ≠ 0"
shows "eventually (λs. fds_converges f s ∧ eval_fds f s ≠ 0) ((λs. s ∙ 1) going_to at_top)"
proof -
from ereal_dense2[OF assms(1)] obtain c where c: "conv_abscissa f < ereal c" by auto
have "eventually (λs::'a. s ∙ 1 > c) ((λs. s ∙ 1) going_to at_top)"
using eventually_gt_at_top[of c] by auto
hence "eventually (λs. fds_converges f s) ((λs. s ∙ 1) going_to at_top)"
by eventually_elim (use c in ‹auto intro!: fds_converges simp: less_le_trans›)
moreover have "eventually (λs. eval_fds f s ≠ 0) ((λs. s ∙ 1) going_to at_top)"
using eval_fds_zeroD[OF assms(1)] assms(2) by (auto simp: frequently_def)
ultimately show ?thesis by (rule eventually_conj)
qed
subsection ‹Normed series›
lemma fds_converges_norm_iff [simp]:
fixes s :: "'a :: {nat_power_normed_field,banach}"
shows "fds_converges (fds_norm f) (s ∙ 1) ⟷ fds_abs_converges f s"
unfolding fds_converges_def fds_abs_converges_def
by (rule summable_cong [OF eventually_mono[OF eventually_gt_at_top[of 0]]])
(simp add: fds_abs_converges_def fds_norm_def fds_nth_fds' norm_divide norm_nat_power)
lemma fds_abs_converges_norm_iff [simp]:
fixes s :: "'a :: {nat_power_normed_field,banach}"
shows "fds_abs_converges (fds_norm f) (s ∙ 1) ⟷ fds_abs_converges f s"
unfolding fds_abs_converges_def
by (rule summable_cong [OF eventually_mono[OF eventually_gt_at_top[of 0]]])
(simp add: fds_abs_converges_def fds_norm_def fds_nth_fds' norm_divide norm_nat_power)
lemma fds_converges_norm_iff':
fixes f :: "'a :: {nat_power_normed_field,banach} fds"
shows "fds_converges (fds_norm f) s ⟷ fds_abs_converges f (of_real s)"
unfolding fds_converges_def fds_abs_converges_def
by (rule summable_cong [OF eventually_mono[OF eventually_gt_at_top[of 0]]])
(simp add: fds_abs_converges_def fds_norm_def fds_nth_fds' norm_divide norm_nat_power)
lemma fds_abs_converges_norm_iff':
fixes f :: "'a :: {nat_power_normed_field,banach} fds"
shows "fds_abs_converges (fds_norm f) s ⟷ fds_abs_converges f (of_real s)"
unfolding fds_abs_converges_def
by (rule summable_cong [OF eventually_mono[OF eventually_gt_at_top[of 0]]])
(simp add: fds_abs_converges_def fds_norm_def fds_nth_fds' norm_divide norm_nat_power)
lemma abs_conv_abscissa_norm [simp]:
fixes f :: "'a :: dirichlet_series fds"
shows "abs_conv_abscissa (fds_norm f) = abs_conv_abscissa f"
proof (rule antisym)
show "abs_conv_abscissa f ≤ abs_conv_abscissa (fds_norm f)"
proof (rule abs_conv_abscissa_leI_weak)
fix x assume "abs_conv_abscissa (fds_norm f) < ereal x"
hence "fds_abs_converges (fds_norm f) (of_real x)" by (intro fds_abs_converges) auto
thus "fds_abs_converges f (of_real x)" by (simp add: fds_abs_converges_norm_iff')
qed
qed (auto intro!: abs_conv_abscissa_leI_weak simp: fds_abs_converges_norm_iff' fds_abs_converges)
lemma conv_abscissa_norm [simp]:
fixes f :: "'a :: dirichlet_series fds"
shows "conv_abscissa (fds_norm f) = abs_conv_abscissa f"
proof (rule antisym)
show "abs_conv_abscissa f ≤ conv_abscissa (fds_norm f)"
proof (rule abs_conv_abscissa_leI_weak)
fix x assume "conv_abscissa (fds_norm f) < ereal x"
hence "fds_converges (fds_norm f) (of_real x)" by (intro fds_converges) auto
thus "fds_abs_converges f (of_real x)" by (simp add: fds_converges_norm_iff')
qed
qed (auto intro!: conv_abscissa_leI_weak simp: fds_abs_converges)
lemma
fixes f g :: "'a :: dirichlet_series fds"
assumes "fds_abs_converges (fds_norm f) s" "fds_abs_converges (fds_norm g) s"
shows fds_abs_converges_norm_mult: "fds_abs_converges (fds_norm (f * g)) s"
and eval_fds_norm_mult_le:
"eval_fds (fds_norm (f * g)) s ≤ eval_fds (fds_norm f) s * eval_fds (fds_norm g) s"
proof -
show conv: "fds_abs_converges (fds_norm (f * g)) s" unfolding fds_abs_converges_def
proof (rule summable_comparison_test_ev)
have "fds_abs_converges (fds_norm f * fds_norm g) s" by (rule fds_abs_converges_mult assms)+
thus "summable (λn. norm (fds_nth (fds_norm f * fds_norm g) n) / nat_power n s)"
by (simp add: fds_abs_converges_def)
qed (auto intro!: always_eventually divide_right_mono order.trans[OF fds_nth_norm_mult_le]
simp: norm_divide)
have conv': "fds_abs_converges (fds_norm f * fds_norm g) s"
by (intro fds_abs_converges_mult assms)
hence "eval_fds (fds_norm (f * g)) s ≤ eval_fds (fds_norm f * fds_norm g) s"
using conv unfolding eval_fds_def fds_abs_converges_def norm_divide
by (intro suminf_le allI divide_right_mono) (simp_all add: norm_mult fds_nth_norm_mult_le)
also have "… = eval_fds (fds_norm f) s * eval_fds (fds_norm g) s"
by (intro eval_fds_mult assms)
finally show "eval_fds (fds_norm (f * g)) s ≤ eval_fds (fds_norm f) s * eval_fds (fds_norm g) s" .
qed
lemma eval_fds_norm_nonneg:
assumes "fds_abs_converges (fds_norm f) s"
shows "eval_fds (fds_norm f) s ≥ 0"
using assms unfolding eval_fds_def fds_abs_converges_def
by (intro suminf_nonneg) auto
lemma
fixes f :: "'a :: dirichlet_series fds"
assumes "fds_abs_converges (fds_norm f) s"
shows fds_abs_converges_norm_power: "fds_abs_converges (fds_norm (f ^ n)) s"
and eval_fds_norm_power_le:
"eval_fds (fds_norm (f ^ n)) s ≤ eval_fds (fds_norm f) s ^ n"
proof -
show *: "fds_abs_converges (fds_norm (f ^ n)) s" for n
by (induction n) (auto intro!: fds_abs_converges_norm_mult assms)
show "eval_fds (fds_norm (f ^ n)) s ≤ eval_fds (fds_norm f) s ^ n"
by (induction n) (auto intro!: order.trans[OF eval_fds_norm_mult_le] assms *
mult_left_mono eval_fds_norm_nonneg)
qed
subsection ‹Logarithms of Dirichlet series›
lemma eventually_gt_ereal_at_top: "c ≠ ∞ ⟹ eventually (λx. ereal x > c) at_top"
by (cases c) auto
lemma eval_fds_log_deriv:
fixes s :: "'a :: dirichlet_series"
assumes "fds_nth f 1 ≠ 0" "s ∙ 1 > abs_conv_abscissa f"
"s ∙ 1 > abs_conv_abscissa (fds_deriv f / f)"
assumes "eval_fds f s ≠ 0"
shows "eval_fds (fds_deriv f / f) s = eval_fds (fds_deriv f) s / eval_fds f s"
proof -
have "eval_fds (fds_deriv f / f * f) s = eval_fds (fds_deriv f / f) s * eval_fds f s"
using assms by (intro eval_fds_mult fds_abs_converges) auto
also have "fds_deriv f / f * f = fds_deriv f * (f * inverse f)"
by (simp add: divide_fds_def algebra_simps)
also have "f * inverse f = 1" using assms by (intro fds_right_inverse)
finally show ?thesis using assms by simp
qed
text ‹
Given a sufficiently nice absolutely convergent Dirichlet series that converges
to some function $f(s)$ and a holomorphic branch of $\ln f(s)$, we can construct
a Dirichlet series that absolutely converges to that logarithm.
›
lemma eval_fds_ln:
fixes s0 :: ereal
assumes nz: "⋀s. Re s > s0 ⟹ eval_fds f s ≠ 0" "fds_nth f 1 ≠ 0"
assumes l: "exp l = fds_nth f 1" "((g ∘ of_real) ⤏ l) at_top"
assumes g: "⋀s. Re s > s0 ⟹ exp (g s) = eval_fds f s"
assumes holo_g: "g holomorphic_on {s. Re s > s0}"
assumes "ereal (Re s) > s0"
assumes "s0 ≥ abs_conv_abscissa f" and "s0 ≥ abs_conv_abscissa (fds_deriv f / f)"
shows "eval_fds (fds_ln l f) s = g s"
proof -
let ?s0 = "abs_conv_abscissa f" and ?s1 = "abs_conv_abscissa (inverse f)"
let ?h = "λs. eval_fds (fds_ln l f) s - g s"
let ?A = "{s. Re s > s0}"
have open_A: "open ?A" by (cases s0) (auto simp: open_halfspace_Re_gt)
have "conv_abscissa f ≤ abs_conv_abscissa f" by (rule conv_le_abs_conv_abscissa)
moreover from assms have "… ≠ ∞" by auto
ultimately have "conv_abscissa f ≠ ∞" by auto
have "conv_abscissa (fds_ln l f) ≤ abs_conv_abscissa (fds_ln l f)"
by (rule conv_le_abs_conv_abscissa)
also have "… ≤ abs_conv_abscissa (fds_deriv f / f)"
unfolding fds_ln_def by (simp add: abs_conv_abscissa_integral)
finally have "conv_abscissa (fds_ln l f) ≠ ∞"
using assms by (auto simp: max_def abs_conv_abscissa_deriv split: if_splits)
have deriv_g [derivative_intros]:
"(g has_field_derivative eval_fds (fds_deriv f) s / eval_fds f s) (at s within B)"
if s: "Re s > s0" for s B
proof -
have "conv_abscissa f ≤ abs_conv_abscissa f" by (rule conv_le_abs_conv_abscissa)
also have "… ≤ s0" using assms by simp
also have "… < Re s" by fact
finally have s': "Re s > conv_abscissa f" .
have deriv_g: "(g has_field_derivative deriv g s) (at s)"
using holomorphic_derivI[OF holo_g open_A, of s] s
by (auto simp: at_within_open[OF _ open_A])
have "((λs. exp (g s)) has_field_derivative eval_fds f s * deriv g s) (at s)" (is ?P)
by (rule derivative_eq_intros deriv_g s)+ (insert s, simp_all add: g)
also from s have ev: "eventually (λt. t ∈ ?A) (nhds s)"
by (intro eventually_nhds_in_open open_A) auto
have "?P ⟷ (eval_fds f has_field_derivative eval_fds f s * deriv g s) (at s)"
by (intro DERIV_cong_ev refl eventually_mono[OF ev]) (auto simp: g)
finally have "(eval_fds f has_field_derivative eval_fds f s * deriv g s) (at s)" .
moreover have "(eval_fds f has_field_derivative eval_fds (fds_deriv f) s) (at s)"
using s' assms by (intro derivative_intros) auto
ultimately have "eval_fds f s * deriv g s = eval_fds (fds_deriv f) s"
by (rule DERIV_unique)
hence "deriv g s = eval_fds (fds_deriv f) s / eval_fds f s"
using s nz by (simp add: field_simps)
with deriv_g show ?thesis by (auto intro: has_field_derivative_at_within)
qed
have "∃c. ∀z∈{z. Re z > s0}. ?h z = c"
proof (rule has_field_derivative_zero_constant, goal_cases)
case 1
show ?case using convex_halfspace_gt[of _ "1::complex"]
by (cases s0) auto
next
case (2 z)
have "conv_abscissa (fds_ln l f) ≤ abs_conv_abscissa (fds_ln l f)"
by (rule conv_le_abs_conv_abscissa)
also have "… ≤ abs_conv_abscissa (fds_deriv f / f)"
by (simp add: abs_conv_abscissa_ln)
also have "… < Re z" using 2 assms by (auto simp: abs_conv_abscissa_deriv)
finally have s1: "conv_abscissa (fds_ln l f) < ereal (Re z)" .
have "conv_abscissa f ≤ abs_conv_abscissa f"
by (rule conv_le_abs_conv_abscissa)
also have "… < Re z" using 2 assms by auto
finally have s2: "conv_abscissa f < ereal (Re z)" .
from l have "fds_nth f 1 ≠ 0" by auto
with 2 assms have *: "eval_fds (fds_deriv f / f) z = eval_fds (fds_deriv f) z / (eval_fds f z)"
by (auto simp: eval_fds_log_deriv)
have "eval_fds f z ≠ 0" using 2 assms by auto
show ?case using s1 s2 2 nz
by (auto intro!: derivative_eq_intros simp: * field_simps)
qed
then obtain c where c: "⋀z. Re z > s0 ⟹ ?h z = c" by blast
have "(at_top :: real filter) ≠ bot" by simp
moreover from assms have "s0 ≠ ∞" by auto
have "eventually (λx. c = (?h ∘ of_real) x) at_top"
using eventually_gt_ereal_at_top[OF ‹s0 ≠ ∞›] by eventually_elim (simp add: c)
hence "((?h ∘ of_real) ⤏ c) at_top"
by (force intro: Lim_transform_eventually)
moreover have "((?h ∘ of_real) ⤏ fds_nth (fds_ln l f) 1 - l) at_top"
using ‹conv_abscissa (fds_ln l f) ≠ ∞› and l unfolding o_def
by (intro tendsto_intros tendsto_eval_fds_Re_at_top) (auto simp: filterlim_ident)
ultimately have "c = fds_nth (fds_ln l f) 1 - l"
by (rule tendsto_unique)
with c[OF ‹Re s > s0›] and l and nz show ?thesis
by (simp add: exp_minus field_simps)
qed
text ‹
Less explicitly: For a sufficiently nice absolutely convergent Dirichlet series converging
to a function $f(s)$, the formal logarithm absolutely converges to some logarithm of $f(s)$.
›
lemma eval_fds_ln':
fixes s0 :: ereal
assumes "ereal (Re s) > s0"
assumes "s0 ≥ abs_conv_abscissa f" and "s0 ≥ abs_conv_abscissa (fds_deriv f / f)"
and nz: "⋀s. Re s > s0 ⟹ eval_fds f s ≠ 0" "fds_nth f 1 ≠ 0"
assumes l: "exp l = fds_nth f 1"
shows "exp (eval_fds (fds_ln l f) s) = eval_fds f s"
proof -
let ?s0 = "abs_conv_abscissa f" and ?s1 = "abs_conv_abscissa (inverse f)"
let ?h = "λs. eval_fds f s * exp (-eval_fds (fds_ln l f) s)"
have "conv_abscissa f ≤ abs_conv_abscissa f" by (rule conv_le_abs_conv_abscissa)
moreover from assms have "… ≠ ∞" by auto
ultimately have "conv_abscissa f ≠ ∞" by auto
have "conv_abscissa (fds_ln l f) ≤ abs_conv_abscissa (fds_ln l f)"
by (rule conv_le_abs_conv_abscissa)
also have "… ≤ abs_conv_abscissa (fds_deriv f / f)"
unfolding fds_ln_def by (simp add: abs_conv_abscissa_integral)
finally have "conv_abscissa (fds_ln l f) ≠ ∞"
using assms by (auto simp: max_def abs_conv_abscissa_deriv split: if_splits)
have "∃c. ∀z∈{z. Re z > s0}. ?h z = c"
proof (rule has_field_derivative_zero_constant, goal_cases)
case 1
show ?case using convex_halfspace_gt[of _ "1::complex"]
by (cases s0) auto
next
case (2 z)
have "conv_abscissa (fds_ln l f) ≤ abs_conv_abscissa (fds_ln l f)"
by (rule conv_le_abs_conv_abscissa)
also have "… ≤ abs_conv_abscissa (fds_deriv f / f)"
unfolding fds_ln_def by (simp add: abs_conv_abscissa_integral)
also have "… < Re z" using 2 assms by (auto simp: abs_conv_abscissa_deriv)
finally have s1: "conv_abscissa (fds_ln l f) < ereal (Re z)" .
have "conv_abscissa f ≤ abs_conv_abscissa f"
by (rule conv_le_abs_conv_abscissa)
also have "… < Re z" using 2 assms by auto
finally have s2: "conv_abscissa f < ereal (Re z)" .
from l have "fds_nth f 1 ≠ 0" by auto
with 2 assms have *: "eval_fds (fds_deriv f / f) z = eval_fds (fds_deriv f) z / (eval_fds f z)"
by (subst eval_fds_log_deriv) auto
have "eval_fds f z ≠ 0" using 2 assms by auto
thus ?case using s1 s2
by (auto intro!: derivative_eq_intros simp: *)
qed
then obtain c where c: "⋀z. Re z > s0 ⟹ ?h z = c" by blast
have "(at_top :: real filter) ≠ bot" by simp
moreover from assms have "s0 ≠ ∞" by auto
have "eventually (λx. c = (?h ∘ of_real) x) at_top"
using eventually_gt_ereal_at_top[OF ‹s0 ≠ ∞›] by eventually_elim (simp add: c)
hence "((?h ∘ of_real) ⤏ c) at_top"
by (force intro: Lim_transform_eventually)
moreover have "((?h ∘ of_real) ⤏ fds_nth f 1 * exp (-fds_nth (fds_ln l f) 1)) at_top"
unfolding o_def using ‹conv_abscissa (fds_ln l f) ≠ ∞› and ‹conv_abscissa f ≠ ∞›
by (intro tendsto_intros tendsto_eval_fds_Re_at_top) (auto simp: filterlim_ident)
ultimately have "c = fds_nth f 1 * exp (-fds_nth (fds_ln l f) 1)"
by (rule tendsto_unique)
with c[OF ‹Re s > s0›] and l and nz show ?thesis
by (simp add: exp_minus field_simps)
qed
lemma fds_ln_completely_multiplicative:
fixes f :: "'a :: dirichlet_series fds"
assumes "completely_multiplicative_function (fds_nth f)"
assumes "fds_nth f 1 ≠ 0"
shows "fds_ln l f = fds (λn. if n = 1 then l else fds_nth f n * mangoldt n /⇩R ln n)"
proof -
have "fds_ln l f = fds_integral l (fds_deriv f / f)"
by (simp add: fds_ln_def)
also have "fds_deriv f = -fds (λn. fds_nth f n * mangoldt n) * f"
by (intro completely_multiplicative_fds_deriv' assms)
also have "… / f = -fds (λn. fds_nth f n * mangoldt n) * (f * inverse f)"
by (simp add: divide_fds_def)
also from assms have "f * inverse f = 1"
by (simp add: fds_right_inverse)
also have "fds_integral l (- fds (λn. fds_nth f n * mangoldt n) * 1) =
fds (λn. if n = 1 then l else fds_nth f n * mangoldt n /⇩R ln n)"
by (simp add: fds_integral_def cong: if_cong)
finally show ?thesis .
qed
lemma eval_fds_ln_completely_multiplicative_strong:
fixes s :: "'a :: dirichlet_series" and l :: 'a and f :: "'a fds" and g :: "nat ⇒ 'a"
defines "h ≡ fds (λn. fds_nth (fds_ln l f) n * g n)"
assumes "fds_abs_converges h s"
assumes "completely_multiplicative_function (fds_nth f)" and "fds_nth f 1 ≠ 0"
shows "(λ(p,k). (fds_nth f p / nat_power p s) ^ Suc k * g (p ^ Suc k) / of_nat (Suc k))
abs_summable_on ({p. prime p} × UNIV)" (is ?th1)
and "eval_fds h s = l * g 1 + (∑⇩a(p, k)∈{p. prime p}×UNIV.
(fds_nth f p / nat_power p s) ^ Suc k * g (p ^ Suc k) / of_nat (Suc k))" (is ?th2)
proof -
let ?P = "{p::nat. prime p}"
interpret f: completely_multiplicative_function "fds_nth f" by fact
from assms have *: "(λn. fds_nth h n / nat_power n s) abs_summable_on UNIV"
by (auto simp: abs_summable_on_nat_iff' fds_abs_converges_def)
have eq: "h = fds (λn. if n = 1 then l * g 1 else fds_nth f n * g n * mangoldt n /⇩R ln (real n))"
using fds_ln_completely_multiplicative [OF assms(3), of l]
by (simp add: h_def fds_eq_iff)
note *
also have "(λn. fds_nth h n / nat_power n s) abs_summable_on UNIV ⟷
(λx. if x = Suc 0 then l * g 1 else fds_nth f x * g x * mangoldt x /⇩R ln (real x) /
nat_power x s) abs_summable_on {1} ∪ Collect primepow"
using eq by (intro abs_summable_on_cong_neutral) (auto simp: fds_nth_fds mangoldt_def)
finally have sum1: "(λx. if x = Suc 0 then l * g 1 else
fds_nth f x * g x * mangoldt x /⇩R ln (real x) / nat_power x s)
abs_summable_on Collect primepow"
by (rule abs_summable_on_subset) auto
also have "?this ⟷ (λx. fds_nth f x * g x * mangoldt x /⇩R ln (real x) / nat_power x s)
abs_summable_on Collect primepow"
by (intro abs_summable_on_cong) (insert primepow_gt_Suc_0, auto)
also have "… ⟷ (λ(p,k). fds_nth f (p ^ Suc k) * g (p ^ Suc k) * mangoldt (p ^ Suc k)
/⇩R ln (real (p ^ Suc k)) / nat_power (p ^ Suc k) s) abs_summable_on (?P × UNIV)"
using bij_betw_primepows unfolding case_prod_unfold
by (intro abs_summable_on_reindex_bij_betw [symmetric])
also have "… ⟷ ?th1"
by (intro abs_summable_on_cong)
(auto simp: f.mult f.power mangoldt_def aprimedivisor_prime_power ln_realpow prime_gt_0_nat
nat_power_power_left divide_simps scaleR_conv_of_real simp del: power_Suc)
finally show ?th1 .
have "eval_fds h s = (∑⇩an. fds_nth h n / nat_power n s)"
using * unfolding eval_fds_def by (subst infsetsum_nat') auto
also have "… = (∑⇩an ∈ {1} ∪ {n. primepow n}.
if n = 1 then l * g 1 else fds_nth f n * g n * mangoldt n /⇩R ln (real n) / nat_power n s)"
by (intro infsetsum_cong_neutral) (auto simp: eq fds_nth_fds mangoldt_def)
also have "… = l * g 1 + (∑⇩an | primepow n.
if n = 1 then l * g 1 else fds_nth f n * g n * mangoldt n /⇩R ln (real n) / nat_power n s)"
(is "_ = _ + ?x") using sum1 primepow_gt_Suc_0 by (subst infsetsum_Un_disjoint) auto
also have "?x =
(∑⇩an∈Collect primepow. fds_nth f n * g n * mangoldt n /⇩R ln (real n) / nat_power n s)"
(is "_ = infsetsum ?f _") by (intro infsetsum_cong refl) (insert primepow_gt_Suc_0, auto)
also have "… = (∑⇩a(p,k)∈(?P × UNIV). fds_nth f (p ^ Suc k) * g (p ^ Suc k) *
mangoldt (p ^ Suc k) /⇩R ln (p ^ Suc k) / nat_power (p ^ Suc k) s)"
using bij_betw_primepows unfolding case_prod_unfold
by (intro infsetsum_reindex_bij_betw [symmetric])
also have "… = (∑⇩a(p,k)∈(?P × UNIV).
(fds_nth f p / nat_power p s) ^ Suc k * g (p ^ Suc k) / of_nat (Suc k))"
by (intro infsetsum_cong)
(auto simp: f.mult f.power mangoldt_def aprimedivisor_prime_power ln_realpow prime_gt_0_nat
nat_power_power_left divide_simps scaleR_conv_of_real simp del: power_Suc)
finally show ?th2 .
qed
lemma eval_fds_ln_completely_multiplicative:
fixes s :: "'a :: dirichlet_series" and l :: 'a and f :: "'a fds"
assumes "completely_multiplicative_function (fds_nth f)" and "fds_nth f 1 ≠ 0"
assumes "s ∙ 1 > abs_conv_abscissa (fds_deriv f / f)"
shows "(λ(p,k). (fds_nth f p / nat_power p s) ^ Suc k / of_nat (Suc k))
abs_summable_on ({p. prime p} × UNIV)" (is ?th1)
and "eval_fds (fds_ln l f) s =
l + (∑⇩a(p, k)∈{p. prime p}×UNIV.
(fds_nth f p / nat_power p s) ^ Suc k / of_nat (Suc k))" (is ?th2)
proof -
from assms have "fds_abs_converges (fds_ln l f) s"
by (intro fds_abs_converges_ln) (auto intro!: fds_abs_converges_mult intro: fds_abs_converges)
hence "fds_abs_converges (fds (λn. fds_nth (fds_ln l f) n * 1)) s"
by simp
from eval_fds_ln_completely_multiplicative_strong [OF this assms(1,2)] show ?th1 ?th2
by simp_all
qed
subsection ‹Exponential and logarithm›
lemma summable_fds_exp_aux:
assumes "fds_nth f' 1 = (0 :: 'a :: real_normed_algebra_1)"
shows "summable (λk. fds_nth (f' ^ k) n /⇩R fact k)"
proof (rule summable_finite)
fix k assume "k ∉ {..n}"
hence "n < k" by simp
also have "… < 2 ^ k"
by (rule less_exp)
finally have "fds_nth (f' ^ k) n = 0"
using assms by (intro fds_nth_power_eq_0) auto
thus "fds_nth (f' ^ k) n /⇩R fact k = 0" by simp
qed auto
lemma
fixes f :: "'a :: dirichlet_series fds"
assumes "fds_abs_converges f s"
shows fds_abs_converges_exp: "fds_abs_converges (fds_exp f) s"
and eval_fds_exp: "eval_fds (fds_exp f) s = exp (eval_fds f s)"
proof -
have conv: "fds_abs_converges (fds_exp f) s" and ev: "eval_fds (fds_exp f) s = exp (eval_fds f s)"
if "fds_abs_converges f s" and [simp]: "fds_nth f (Suc 0) = 0" for f
proof -
have [simp]: "fds (λn. if n = Suc 0 then 0 else fds_nth f n) = f"
by (intro fds_eqI) simp_all
have "(λ(k,n). fds_nth (f ^ k) n / fact k / nat_power n s) abs_summable_on (UNIV × {1..})"
proof (subst abs_summable_on_Sigma_iff, safe, goal_cases)
case (3 k)
from that have "fds_abs_converges (f ^ k) s" by (intro fds_abs_converges_power)
hence "(λn. fds_nth (f ^ k) n / nat_power n s * inverse (fact k)) abs_summable_on {1..}"
unfolding fds_abs_converges_altdef by (intro abs_summable_on_cmult_left)
thus ?case by (simp add: field_simps)
next
case 4
show ?case unfolding abs_summable_on_nat_iff'
proof (rule summable_comparison_test_ev[OF always_eventually[OF allI]])
fix k :: nat
from that have *: "fds_abs_converges (fds_norm (f ^ k)) (s ∙ 1)"
by (auto simp: fds_abs_converges_power)
have "(∑⇩an∈{1..}. norm (fds_nth (f ^ k) n / fact k / nat_power n s)) =
(∑⇩an∈{1..}. fds_nth (fds_norm (f ^ k)) n / nat_power n (s ∙ 1) / fact k)"
(is "?S = _") by (intro infsetsum_cong) (simp_all add: norm_divide norm_mult norm_nat_power)
also have "… = (∑⇩an∈{1..}. fds_nth (fds_norm (f ^ k)) n / nat_power n (s ∙ 1)) /⇩R fact k"
(is "_ = ?S' /⇩R _") using * unfolding fds_abs_converges_altdef
by (subst infsetsum_cdiv) (auto simp: abs_summable_on_nat_iff scaleR_conv_of_real divide_simps)
also have "?S' = eval_fds (fds_norm (f ^ k)) (s ∙ 1)"
using * unfolding fds_abs_converges_altdef eval_fds_def
by (subst infsetsum_nat) (auto intro!: suminf_cong)
finally have eq: "?S = … /⇩R fact k" .
note eq
also have "?S ≥ 0" by (intro infsetsum_nonneg) auto
hence "?S = norm (norm ?S)" by simp
also have "eval_fds (fds_norm (f ^ k)) (s ∙ 1) ≤ eval_fds (fds_norm f) (s ∙ 1) ^ k"
using that by (intro eval_fds_norm_power_le) auto
finally show "norm (norm (∑⇩an∈{1..}. norm (fds_nth (f ^ k) n / fact k / nat_power n s))) ≤
eval_fds (fds_norm f) (s ∙ 1) ^ k /⇩R fact k"
by (simp add: divide_right_mono)
next
from exp_converges[of "eval_fds (fds_norm f) (s ∙ 1)"]
show "summable (λx. eval_fds (fds_norm f) (s ∙ 1) ^ x /⇩R fact x)"
by (simp add: sums_iff)
qed
qed auto
hence summable:
"(λ(n,k). fds_nth (f ^ k) n / fact k / nat_power n s) abs_summable_on {1..} × UNIV"
by (subst abs_summable_on_Times_swap) (simp add: case_prod_unfold)
have summable': "(λk. fds_nth (f ^ k) n / fact k) abs_summable_on UNIV" for n
using abs_summable_on_cmult_left[of "nat_power n s",
OF abs_summable_on_Sigma_project2 [OF summable, of n]] by (cases "n = 0") simp_all
have "(λn. ∑⇩ak. fds_nth (f ^ k) n / fact k / nat_power n s) abs_summable_on {1..}"
using summable by (rule abs_summable_on_Sigma_project1') auto
also have "?this ⟷ (λn. (∑k. fds_nth (f ^ k) n / fact k) * inverse (nat_power n s))
abs_summable_on {1..}"
proof (intro abs_summable_on_cong refl, goal_cases)
case (1 n)
hence "(∑⇩ak. fds_nth (f ^ k) n / fact k / nat_power n s) =
(∑⇩ak. fds_nth (f ^ k) n / fact k) * inverse (nat_power n s)"
using summable'[of n]
by (subst infsetsum_cmult_left [symmetric]) (auto simp: field_simps)
also have "(∑⇩ak. fds_nth (f ^ k) n / fact k) = (∑k. fds_nth (f ^ k) n / fact k)"
using summable'[of n] 1 by (intro abs_summable_on_cong refl infsetsum_nat') auto
finally show ?case .
qed
finally show "fds_abs_converges (fds_exp f) s"
by (simp add: fds_exp_def fds_nth_fds' abs_summable_on_Sigma_iff scaleR_conv_of_real
fds_abs_converges_altdef field_simps)
have "eval_fds (fds_exp f) s = (∑n. (∑k. fds_nth (f ^ k) n /⇩R fact k) / nat_power n s)"
by (simp add: fds_exp_def eval_fds_def fds_nth_fds')
also have "… = (∑n. (∑⇩ak. fds_nth (f ^ k) n /⇩R fact k) / nat_power n s)"
proof (intro suminf_cong, goal_cases)
case (1 n)
show ?case
proof (cases "n = 0")
case False
have "(∑k. fds_nth (f ^ k) n /⇩R fact k) = (∑⇩ak. fds_nth (f ^ k) n /⇩R fact k)"
using summable'[of n] False
by (intro infsetsum_nat' [symmetric]) (auto simp: scaleR_conv_of_real field_simps)
thus ?thesis by simp
qed simp_all
qed
also have "… = (∑⇩an. (∑⇩ak. fds_nth (f ^ k) n /⇩R fact k) / nat_power n s)"
proof (intro infsetsum_nat' [symmetric], goal_cases)
case 1
have *: "UNIV - {Suc 0..} = {0}" by auto
have "(λx. ∑⇩ay. fds_nth (f ^ y) x / fact y / nat_power x s) abs_summable_on {1..}"
by (intro abs_summable_on_Sigma_project1'[OF summable]) auto
also have "?this ⟷ (λx. (∑⇩ay. fds_nth (f ^ y) x / fact y) * inverse (nat_power x s))
abs_summable_on {1..}"
using summable' by (intro abs_summable_on_cong refl, subst infsetsum_cmult_left [symmetric])
(auto simp: field_simps)
also have "… ⟷ (λx. (∑⇩ay. fds_nth (f ^ y) x /⇩R fact y) / (nat_power x s))
abs_summable_on {1..}" by (simp add: field_simps scaleR_conv_of_real)
finally show ?case by (rule abs_summable_on_finite_diff) (use * in auto)
qed
also have "… = (∑⇩an. (∑⇩ak. fds_nth (f ^ k) n /⇩R fact k * inverse (nat_power n s)))"
using summable' by (subst infsetsum_cmult_left) (auto simp: field_simps scaleR_conv_of_real)
also have "… = (∑⇩an∈{1..}. (∑⇩ak. fds_nth (f ^ k) n /⇩R fact k * inverse (nat_power n s)))"
by (intro infsetsum_cong_neutral) (auto simp: Suc_le_eq)
also have "… = (∑⇩ak. ∑⇩an∈{1..}. fds_nth (f ^ k) n / nat_power n s /⇩R fact k)" using summable
by (subst infsetsum_swap) (auto simp: field_simps scaleR_conv_of_real case_prod_unfold)
also have "… = (∑⇩ak. (∑⇩an∈{1..}. fds_nth (f ^ k) n / nat_power n s) /⇩R fact k)"
by (subst infsetsum_scaleR_right) simp
also have "… = (∑⇩ak. eval_fds f s ^ k /⇩R fact k)"
proof (intro infsetsum_cong refl, goal_cases)
case (1 k)
have *: "fds_abs_converges (f ^ k) s" by (intro fds_abs_converges_power that)
have "(∑⇩an∈{1..}. fds_nth (f ^ k) n / nat_power n s) =
(∑⇩an. fds_nth (f ^ k) n / nat_power n s)"
by (intro infsetsum_cong_neutral) (auto simp: Suc_le_eq)
also have "… = eval_fds (f ^ k) s" using * unfolding eval_fds_def
by (intro infsetsum_nat') (auto simp: fds_abs_converges_def abs_summable_on_nat_iff')
also from that have "… = eval_fds f s ^ k" by (simp add: eval_fds_power)
finally show ?case by simp
qed
also have "… = (∑k. eval_fds f s ^ k /⇩R fact k)"
using exp_converges[of "norm (eval_fds f s)"]
by (intro infsetsum_nat') (auto simp: abs_summable_on_nat_iff' sums_iff field_simps norm_power)
also have "… = exp (eval_fds f s)" by (simp add: exp_def)
finally show "eval_fds (fds_exp f) s = exp (eval_fds f s)" .
qed
define f' where "f' = f - fds_const (fds_nth f 1)"
have *: "fds_abs_converges (fds_exp f') s"
by (auto simp: f'_def intro!: fds_abs_converges_diff conv assms)
have "fds_abs_converges (fds_const (exp (fds_nth f 1)) * fds_exp f') s"
unfolding f'_def
by (intro fds_abs_converges_mult conv fds_abs_converges_diff assms) auto
thus "fds_abs_converges (fds_exp f) s" unfolding f'_def
by (simp add: fds_exp_times_fds_nth_0)
have "eval_fds (fds_exp f) s = eval_fds (fds_const (exp (fds_nth f 1)) * fds_exp f') s"
by (simp add: f'_def fds_exp_times_fds_nth_0)
also have "… = exp (fds_nth f (Suc 0)) * eval_fds (fds_exp f') s" using *
using assms by (subst eval_fds_mult) (simp_all)
also have "… = exp (eval_fds f s)" using ev[of f'] assms unfolding f'_def
by (auto simp: fds_abs_converges_diff eval_fds_diff fds_abs_converges_imp_converges exp_diff)
finally show "eval_fds (fds_exp f) s = exp (eval_fds f s)" .
qed
lemma fds_exp_add:
fixes f :: "'a :: dirichlet_series fds"
shows "fds_exp (f + g) = fds_exp f * fds_exp g"
proof (rule fds_eqI_truncate)
fix m :: nat assume m: "m > 0"
let ?T = "fds_truncate m"
have "?T (fds_exp (f + g)) = ?T (fds_exp (?T f + ?T g))"
by (simp add: fds_truncate_exp fds_truncate_add_strong [symmetric])
also have "fds_exp (?T f + ?T g) = fds_exp (?T f) * fds_exp (?T g)"
proof (rule eval_fds_eqD)
have "fds_abs_converges (fds_exp (?T f + ?T g)) 0"
by (intro fds_abs_converges_exp fds_abs_converges_add) auto
thus "conv_abscissa (fds_exp (?T f + ?T g)) < ∞"
using conv_abscissa_PInf_iff by blast
hence "fds_abs_converges (fds_exp (fds_truncate m f) * fds_exp (fds_truncate m g)) 0"
by (intro fds_abs_converges_mult fds_abs_converges_exp) auto
thus "conv_abscissa (fds_exp (fds_truncate m f) * fds_exp (fds_truncate m g)) < ∞"
using conv_abscissa_PInf_iff by blast
show "frequently (λs. eval_fds (fds_exp (fds_truncate m f + fds_truncate m g)) s =
eval_fds (fds_exp (fds_truncate m f) * fds_exp (fds_truncate m g)) s)
((λs. s ∙ 1) going_to at_top)"
by (auto simp: eval_fds_add eval_fds_mult eval_fds_exp fds_abs_converges_add
fds_abs_converges_exp exp_add)
qed
also have "?T … = ?T (fds_exp f * fds_exp g)"
by (subst fds_truncate_mult [symmetric], subst (1 2) fds_truncate_exp)
(simp add: fds_truncate_mult)
finally show "?T (fds_exp (f + g)) = …" .
qed
lemma fds_exp_minus:
fixes f :: "'a :: dirichlet_series fds"
shows "fds_exp (-f) = inverse (fds_exp f)"
proof (rule fds_right_inverse_unique)
have "fds_exp f * fds_exp (- f) = fds_exp (f + (-f))"
by (subst fds_exp_add) simp_all
also have "f + (-f) = 0" by simp
also have "fds_exp … = 1" by simp
finally show "fds_exp f * fds_exp (-f) = 1" .
qed
lemma abs_conv_abscissa_exp:
fixes f :: "'a :: dirichlet_series fds"
shows "abs_conv_abscissa (fds_exp f) ≤ abs_conv_abscissa f"
by (intro abs_conv_abscissa_mono fds_abs_converges_exp)
lemma fds_deriv_exp [simp]:
fixes f :: "'a :: dirichlet_series fds"
shows "fds_deriv (fds_exp f) = fds_exp f * fds_deriv f"
proof (rule fds_eqI_truncate)
fix m :: nat assume m: "m > 0"
let ?T = "fds_truncate m"
have "abs_conv_abscissa (fds_deriv (?T f)) = -∞"
by (simp add: abs_conv_abscissa_deriv)
have "?T (fds_deriv (fds_exp f)) = ?T (fds_deriv (fds_exp (?T f)))"
by (simp add: fds_truncate_deriv fds_truncate_exp)
also have "fds_deriv (fds_exp (?T f)) = fds_exp (?T f) * fds_deriv (?T f)"
proof (rule eval_fds_eqD)
note abscissa = conv_le_abs_conv_abscissa abs_conv_abscissa_exp
note abscissa' = abscissa[THEN le_less_trans]
have "fds_abs_converges (fds_deriv (fds_exp (fds_truncate m f))) 0"
by (intro fds_abs_converges )
(auto simp: abs_conv_abscissa_deriv intro: le_less_trans[OF abs_conv_abscissa_exp])
thus "conv_abscissa (fds_deriv (fds_exp (fds_truncate m f))) < ∞"
using conv_abscissa_PInf_iff by blast
have "fds_abs_converges (fds_exp (fds_truncate m f) * fds_deriv (fds_truncate m f)) 0"
by (intro fds_abs_converges_mult fds_abs_converges_exp)
(auto intro: fds_abs_converges simp add: fds_truncate_deriv [symmetric])
thus "conv_abscissa (fds_exp (fds_truncate m f) * fds_deriv (fds_truncate m f)) < ∞"
using conv_abscissa_PInf_iff by blast
show "∃⇩F s in (λs. s ∙ 1) going_to at_top.
eval_fds (fds_deriv (fds_exp (?T f))) s =
eval_fds (fds_exp (?T f) * fds_deriv (?T f)) s"
proof (intro always_eventually eventually_frequently allI, goal_cases)
case (2 s)
have "eval_fds (fds_deriv (fds_exp (?T f))) s =
deriv (eval_fds (fds_exp (?T f))) s"
by (auto simp: eval_fds_exp eval_fds_mult fds_abs_converges_mult fds_abs_converges_exp
fds_abs_converges eval_fds_deriv abscissa')
also have "eval_fds (fds_exp (?T f)) = (λs. exp (eval_fds (?T f) s))"
by (intro ext eval_fds_exp) auto
also have "deriv … = (λs. exp (eval_fds (?T f) s) * deriv (eval_fds (?T f)) s)"
by (auto intro!: DERIV_imp_deriv derivative_eq_intros simp: eval_fds_deriv)
also have "… = eval_fds (fds_exp (?T f) * fds_deriv (?T f))"
by (auto simp: eval_fds_exp eval_fds_mult fds_abs_converges_mult fds_abs_converges_exp
fds_abs_converges eval_fds_deriv abs_conv_abscissa_deriv)
finally show ?case .
qed auto
qed
also have "?T … = ?T (fds_exp f * fds_deriv f)"
by (subst fds_truncate_mult [symmetric])
(simp add: fds_truncate_exp fds_truncate_deriv [symmetric], simp add: fds_truncate_mult)
finally show "?T (fds_deriv (fds_exp f)) = …" .
qed
lemma fds_exp_ln_strong:
fixes f :: "'a :: dirichlet_series fds"
assumes "fds_nth f (Suc 0) ≠ 0"
shows "fds_exp (fds_ln l f) = fds_const (exp l / fds_nth f (Suc 0)) * f"
proof -
let ?c = "exp l / fds_nth f (Suc 0)"
have "f * fds_const ?c = f * (fds_exp (-fds_ln l f) * fds_exp (fds_ln l f)) * fds_const ?c"
(is "_ = _ * (?g * ?h) * _") by (subst fds_exp_add [symmetric]) simp
also have "… = fds_const ?c * (f * ?g) * ?h" by (simp add: mult_ac)
also have "f * ?g = fds_const (inverse ?c)"
proof (rule fds_deriv_eq_imp_eq)
have "fds_deriv (f * fds_exp (-fds_ln l f)) =
fds_exp (- fds_ln l f) * fds_deriv f * (1 - f / f)"
by (simp add: divide_fds_def algebra_simps)
also from assms have "f / f = 1" by (simp add: divide_fds_def fds_right_inverse)
finally show "fds_deriv (f * fds_exp (-fds_ln l f)) = fds_deriv (fds_const (inverse ?c))"
by simp
qed (insert assms, auto simp: exp_minus field_simps)
also have "fds_const ?c * fds_const (inverse ?c) = 1"
using assms by (subst fds_const_mult [symmetric]) (simp add: divide_simps)
finally show ?thesis by (simp add: mult_ac)
qed
lemma fds_exp_ln [simp]:
fixes f :: "'a :: dirichlet_series fds"
assumes "exp l = fds_nth f (Suc 0)"
shows "fds_exp (fds_ln l f) = f"
using assms by (subst fds_exp_ln_strong) auto
lemma fds_ln_exp [simp]:
fixes f :: "'a :: dirichlet_series fds"
assumes "l = fds_nth f (Suc 0)"
shows "fds_ln l (fds_exp f) = f"
proof (rule fds_deriv_eq_imp_eq)
have "fds_deriv (fds_ln l (fds_exp f)) = fds_deriv f * (fds_exp f / fds_exp f)"
by (simp add: algebra_simps divide_fds_def)
also have "fds_exp f / fds_exp f = 1" by (simp add: divide_fds_def fds_right_inverse)
finally show "fds_deriv (fds_ln l (fds_exp f)) = fds_deriv f" by simp
qed (insert assms, auto simp: field_simps)
subsection ‹Euler products›
lemma fds_euler_product_LIMSEQ:
fixes f :: "'a :: {nat_power, real_normed_field, banach, second_countable_topology} fds"
assumes "multiplicative_function (fds_nth f)" and "fds_abs_converges f s"
shows "(λn. ∏p≤n. if prime p then ∑i. fds_nth f (p ^ i) / nat_power (p ^ i) s else 1) ⇢
eval_fds f s"
unfolding eval_fds_def
proof (rule euler_product_LIMSEQ)
show "multiplicative_function (λn. fds_nth f n / nat_power n s)"
by (rule multiplicative_function_divide_nat_power) fact+
qed (insert assms, auto simp: fds_abs_converges_def)
lemma fds_euler_product_LIMSEQ':
fixes f :: "'a :: {nat_power, real_normed_field, banach, second_countable_topology} fds"
assumes "completely_multiplicative_function (fds_nth f)" and "fds_abs_converges f s"
shows "(λn. ∏p≤n. if prime p then inverse (1 - fds_nth f p / nat_power p s) else 1) ⇢
eval_fds f s"
unfolding eval_fds_def
proof (rule euler_product_LIMSEQ')
show "completely_multiplicative_function (λn. fds_nth f n / nat_power n s)"
by (rule completely_multiplicative_function_divide_nat_power) fact+
qed (insert assms, auto simp: fds_abs_converges_def)
lemma fds_abs_convergent_euler_product:
fixes f :: "'a :: {nat_power, real_normed_field, banach, second_countable_topology} fds"
assumes "multiplicative_function (fds_nth f)" and "fds_abs_converges f s"
shows "abs_convergent_prod
(λp. if prime p then ∑i. fds_nth f (p ^ i) / nat_power (p ^ i) s else 1)"
unfolding eval_fds_def
proof (rule abs_convergent_euler_product)
show "multiplicative_function (λn. fds_nth f n / nat_power n s)"
by (rule multiplicative_function_divide_nat_power) fact+
qed (insert assms, auto simp: fds_abs_converges_def)
lemma fds_abs_convergent_euler_product':
fixes f :: "'a :: {nat_power, real_normed_field, banach, second_countable_topology} fds"
assumes "completely_multiplicative_function (fds_nth f)" and "fds_abs_converges f s"
shows "abs_convergent_prod
(λp. if prime p then inverse (1 - fds_nth f p / nat_power p s) else 1)"
unfolding eval_fds_def
proof (rule abs_convergent_euler_product')
show "completely_multiplicative_function (λn. fds_nth f n / nat_power n s)"
by (rule completely_multiplicative_function_divide_nat_power) fact+
qed (insert assms, auto simp: fds_abs_converges_def)
lemma fds_abs_convergent_zero_iff:
fixes f :: "'a :: {nat_power_field, real_normed_field, banach, second_countable_topology} fds"
assumes "completely_multiplicative_function (fds_nth f)"
assumes "fds_abs_converges f s"
shows "eval_fds f s = 0 ⟷ (∃p. prime p ∧ fds_nth f p = nat_power p s)"
proof -
let ?g = "λp. if prime p then inverse (1 - fds_nth f p / nat_power p s) else 1"
have lim: "(λn. ∏p≤n. ?g p) ⇢ eval_fds f s"
by (intro fds_euler_product_LIMSEQ' assms)
have conv: "convergent_prod ?g"
by (intro abs_convergent_prod_imp_convergent_prod fds_abs_convergent_euler_product' assms)
{
assume "eval_fds f s = 0"
from convergent_prod_to_zero_iff[OF conv] and this and lim
have "∃p. prime p ∧ fds_nth f p = nat_power p s"
by (auto split: if_splits)
} moreover {
assume "∃p. prime p ∧ fds_nth f p = nat_power p s"
then obtain p where "prime p" "fds_nth f p = nat_power p s" by blast
moreover from this have "nat_power p s ≠ 0"
by (intro nat_power_nonzero) (auto simp: prime_gt_0_nat)
ultimately have "(λn. ∏p≤n. ?g p) ⇢ 0"
using convergent_prod_to_zero_iff[OF conv]
by (auto intro!: exI[of _ p] split: if_splits)
from tendsto_unique[OF _ lim this] have "eval_fds f s = 0"
by simp
}
ultimately show ?thesis by blast
qed
lemma
fixes s :: "'a :: {nat_power_normed_field,banach,euclidean_space}"
assumes "s ∙ 1 > 1"
shows euler_product_fds_zeta:
"(λn. ∏p≤n. if prime p then inverse (1 - 1 / nat_power p s) else 1)
⇢ eval_fds fds_zeta s" (is ?th1)
and eval_fds_zeta_nonzero: "eval_fds fds_zeta s ≠ 0"
proof -
have *: "completely_multiplicative_function (fds_nth fds_zeta)"
by standard auto
have lim: "(λn. ∏p≤n. if prime p then inverse (1 - fds_nth fds_zeta p / nat_power p s) else 1)
⇢ eval_fds fds_zeta s" (is "filterlim ?g _ _")
using assms by (intro fds_euler_product_LIMSEQ' * fds_abs_summable_zeta)
also have "?g = (λn. ∏p≤n. if prime p then inverse (1 - 1 / nat_power p s) else 1)"
by (intro ext prod.cong refl) (auto simp: fds_zeta_def fds_nth_fds)
finally show ?th1 .
{
fix p :: nat assume "prime p"
from this have "p > 1" by (simp add: prime_gt_Suc_0_nat)
hence "norm (nat_power p s) = real p powr (s ∙ 1)"
by (simp add: norm_nat_power)
also have "… > real p powr 0" using assms and ‹p > 1›
by (intro powr_less_mono) auto
finally have "nat_power p s ≠ 1"
using ‹p > 1› by auto
}
hence **: "∄p. prime p ∧ fds_nth fds_zeta p = nat_power p s"
by (auto simp: fds_zeta_def fds_nth_fds)
show "eval_fds fds_zeta s ≠ 0"
using assms * ** by (subst fds_abs_convergent_zero_iff) simp_all
qed
lemma fds_primepow_subseries_euler_product_cm:
fixes f :: "'a :: dirichlet_series fds"
assumes "completely_multiplicative_function (fds_nth f)" "prime p"
assumes "s ∙ 1 > abs_conv_abscissa f"
shows "eval_fds (fds_primepow_subseries p f) s = 1 / (1 - fds_nth f p / nat_power p s)"
proof -
let ?f = "(λn. ∏pa≤n. if prime pa then inverse (1 - fds_nth (fds_primepow_subseries p f) pa /
nat_power pa s) else 1)"
have "sequentially ≠ bot" by simp
moreover have "?f ⇢ eval_fds (fds_primepow_subseries p f) s"
by (intro fds_euler_product_LIMSEQ' completely_multiplicative_function_only_pows assms
fds_abs_converges_subseries) (insert assms, auto intro!: fds_abs_converges)
moreover have "eventually (λn. ?f n = 1 / (1 - fds_nth f p / nat_power p s)) at_top"
using eventually_ge_at_top[of p]
proof eventually_elim
case (elim n)
have "(∏pa≤n. if prime pa then inverse (1 - fds_nth (fds_primepow_subseries p f) pa /
nat_power pa s) else 1) =
(∏q≤n. if q = p then inverse (1 - fds_nth f p / nat_power p s) else 1)" using ‹prime p›
by (intro prod.cong) (auto simp: fds_nth_subseries prime_prime_factors)
also have "… = 1 / (1 - fds_nth f p / nat_power p s)"
using elim by (subst prod.delta) (auto simp: divide_simps)
finally show ?case .
qed
hence "?f ⇢ 1 / (1 - fds_nth f p / nat_power p s)" by (rule tendsto_eventually)
ultimately show ?thesis by (rule tendsto_unique)
qed
subsection ‹Non-negative Dirichlet series›
lemma nonneg_Reals_sum: "(⋀x. x ∈ A ⟹ f x ∈ ℝ⇩≥⇩0) ⟹ sum f A ∈ ℝ⇩≥⇩0"
by (induction A rule: infinite_finite_induct) auto
locale nonneg_dirichlet_series =
fixes f :: "'a :: dirichlet_series fds"
assumes nonneg_coeffs_aux: "n > 0 ⟹ fds_nth f n ∈ ℝ⇩≥⇩0"
begin
lemma nonneg_coeffs: "fds_nth f n ∈ ℝ⇩≥⇩0"
using nonneg_coeffs_aux[of n] by (cases "n = 0") auto
end
lemma nonneg_dirichlet_series_0 [simp,intro]: "nonneg_dirichlet_series 0"
by standard (auto simp: zero_fds_def)
lemma nonneg_dirichlet_series_1 [simp,intro]: "nonneg_dirichlet_series 1"
by standard (auto simp: one_fds_def)
lemma nonneg_dirichlet_series_const [simp,intro]:
"c ∈ ℝ⇩≥⇩0 ⟹ nonneg_dirichlet_series (fds_const c)"
by standard (auto simp: fds_const_def)
lemma nonneg_dirichlet_series_add [intro]:
assumes "nonneg_dirichlet_series f" "nonneg_dirichlet_series g"
shows "nonneg_dirichlet_series (f + g)"
proof -
interpret f: nonneg_dirichlet_series f by fact
interpret g: nonneg_dirichlet_series g by fact
show ?thesis
by standard (auto intro!: nonneg_Reals_add_I f.nonneg_coeffs g.nonneg_coeffs)
qed
lemma nonneg_dirichlet_series_mult [intro]:
assumes "nonneg_dirichlet_series f" "nonneg_dirichlet_series g"
shows "nonneg_dirichlet_series (f * g)"
proof -
interpret f: nonneg_dirichlet_series f by fact
interpret g: nonneg_dirichlet_series g by fact
show ?thesis
by standard (auto intro!: nonneg_Reals_sum nonneg_Reals_mult_I f.nonneg_coeffs g.nonneg_coeffs
simp: fds_nth_mult dirichlet_prod_def)
qed
lemma nonneg_dirichlet_series_power [intro]:
assumes "nonneg_dirichlet_series f"
shows "nonneg_dirichlet_series (f ^ n)"
using assms by (induction n) auto
context nonneg_dirichlet_series
begin
lemma nonneg_exp [intro]: "nonneg_dirichlet_series (fds_exp f)"
proof
fix n :: nat assume "n > 0"
define c where "c = exp (fds_nth f (Suc 0))"
define f' where "f' = fds (λn. if n = Suc 0 then 0 else fds_nth f n)"
from nonneg_coeffs[of 1] obtain c' where "fds_nth f (Suc 0) = of_real c'"
by (auto elim!: nonneg_Reals_cases)
hence "c = of_real (exp c')" by (simp add: c_def exp_of_real)
hence c: "c ∈ ℝ⇩≥⇩0" by simp
have less: "n < 2 ^ k" if "n < k" for k
proof -
have "n < k" by fact
also have "… < 2 ^ k"
by (rule less_exp)
finally show ?thesis .
qed
have nonneg_power: "fds_nth (f' ^ k) n ∈ ℝ⇩≥⇩0" for k
proof -
have "nonneg_dirichlet_series f'"
by standard (insert nonneg_coeffs, auto simp: f'_def)
interpret nonneg_dirichlet_series "f' ^ k"
by (intro nonneg_dirichlet_series_power) fact+
from nonneg_coeffs[of n] show ?thesis .
qed
hence "fds_nth (fds_exp f) n = c * (∑k. fds_nth (f' ^ k) n /⇩R fact k)"
by (simp add: fds_exp_def fds_nth_fds' f'_def c_def)
also have "(∑k. fds_nth (f' ^ k) n /⇩R fact k) = (∑k≤n. fds_nth (f' ^ k) n /⇩R fact k)"
by (intro suminf_finite) (auto intro!: fds_nth_power_eq_0 less simp: f'_def not_le)
also have "c * … ∈ ℝ⇩≥⇩0" unfolding scaleR_conv_of_real
by (intro nonneg_Reals_mult_I nonneg_Reals_sum nonneg_power, unfold nonneg_Reals_of_real_iff )
(auto simp: c)
finally show "fds_nth (fds_exp f) n ∈ ℝ⇩≥⇩0" .
qed
end
lemma nonneg_dirichlet_series_lnD:
assumes "nonneg_dirichlet_series (fds_ln l f)" "exp l = fds_nth f (Suc 0)"
shows "nonneg_dirichlet_series f"
proof -
from assms have "nonneg_dirichlet_series (fds_exp (fds_ln l f))"
by (intro nonneg_dirichlet_series.nonneg_exp)
thus ?thesis using assms by simp
qed
context nonneg_dirichlet_series
begin
lemma fds_of_real_norm: "fds_of_real (fds_norm f) = f"
proof (rule fds_eqI)
fix n :: nat assume n: "n > 0"
show "fds_nth (fds_of_real (fds_norm f)) n = fds_nth f n"
using nonneg_coeffs[of n] by (auto elim!: nonneg_Reals_cases)
qed
end
lemma pringsheim_landau_aux:
fixes c :: real and f :: "complex fds"
assumes "nonneg_dirichlet_series f"
assumes abscissa: "c ≥ abs_conv_abscissa f"
assumes g: "⋀s. s ∈ A ⟹ Re s > c ⟹ g s = eval_fds f s"
assumes "g holomorphic_on A" "open A" "c ∈ A"
shows "∃x. x < c ∧ fds_abs_converges f (of_real x)"
proof -
interpret nonneg_dirichlet_series f by fact
define a where "a = 1 + c"
define g' where "g' = (λs. if s ∈ {s. Re s > c} then eval_fds f s else g s)"
from ‹open A› ‹c ∈ A› obtain δ where δ: "δ > 0" "ball c δ ⊆ A"
by (auto simp: open_contains_ball)
define ε where "ε = sqrt (1 + δ^2) - 1"
from δ have ε: "ε > 0" by (simp add: ε_def)
have ball_a_subset: "ball a (1 + ε) ⊆ {s. Re s > c} ∪ A"
proof (intro subsetI)
fix s :: complex assume s: "s ∈ ball a (1 + ε)"
define x y where "x = Re s" and "y = Im s"
have [simp]: "s = x + 𝗂 * y" by (simp add: complex_eq_iff x_def y_def)
show "s ∈ {s. Re s > c} ∪ A"
proof (cases "Re s ≤ c")
case True
hence "(c - x)⇧2 + y⇧2 ≤ (1 + c - x)⇧2 + y⇧2 - 1"
by (simp add: power2_eq_square algebra_simps)
also from s have "(1 + c - x)⇧2 + y⇧2 - 1 < δ⇧2"
by (auto simp: dist_norm cmod_def a_def ε_def)
finally have "sqrt ((c - x)⇧2 + y⇧2) < δ" using δ
by (intro real_less_lsqrt) auto
hence "s ∈ ball c δ" by (auto simp: dist_norm cmod_def)
also have "… ⊆ A" by fact
finally show ?thesis ..
qed auto
qed
have holo: "g' holomorphic_on ball a (1 + ε)" unfolding g'_def
proof (intro holomorphic_on_subset[OF _ ball_a_subset] holomorphic_on_If_Un)
have "conv_abscissa f ≤ abs_conv_abscissa f" by (rule conv_le_abs_conv_abscissa)
also have "… ≤ ereal c" by fact
finally have*: "conv_abscissa f ≤ ereal c" .
show "eval_fds f holomorphic_on {s. c < Re s}"
by (intro holomorphic_intros) (auto intro: le_less_trans[OF *])
qed (insert assms, auto intro!: holomorphic_intros open_halfspace_Re_gt)
define f' where "f' = fds_norm f"
have f_f': "f = fds_of_real f'" by (simp add: f'_def fds_of_real_norm)
have f'_nonneg: "fds_nth f' n ≥ 0" for n
using nonneg_coeffs[of n] by (auto elim!: nonneg_Reals_cases simp: f'_def)
have deriv: "(λn. (deriv ^^ n) g' a) = (λn. eval_fds ((fds_deriv ^^ n) f) a)"
proof
fix n :: nat
have ev: "eventually (λs. s ∈ {s. Re s > c}) (nhds (complex_of_real a))"
by (intro eventually_nhds_in_open open_halfspace_Re_gt) (auto simp: a_def)
have "(deriv ^^ n) g' a = (deriv ^^ n) (eval_fds f) a"
by (intro higher_deriv_cong_ev refl eventually_mono[OF ev]) (auto simp: g'_def)
also have "… = eval_fds ((fds_deriv ^^ n) f) a"
proof (intro eval_fds_higher_deriv [symmetric])
have "conv_abscissa f ≤ abs_conv_abscissa f" by (rule conv_le_abs_conv_abscissa)
also have "… ≤ ereal c" by (rule assms)
also have "… < a" by (simp add: a_def)
finally show "conv_abscissa f < ereal (complex_of_real a ∙ 1)" by simp
qed
finally show "(deriv ^^ n) g' a = eval_fds ((fds_deriv ^^ n) f) a" .
qed
have nth_deriv_conv: "fds_abs_converges ((fds_deriv ^^ n) f) (of_real a)" for n
by (intro fds_abs_converges)
(auto simp: abs_conv_abscissa_higher_deriv a_def intro!: le_less_trans[OF abscissa])
have nth_deriv_eq: "(fds_deriv ^^ n) f = fds (λk. (-1) ^ n * fds_nth f k * ln (real k) ^ n)" for n
proof -
have "fds_nth ((fds_deriv ^^ n) f) k = (-1) ^ n * fds_nth f k * ln (real k) ^ n" for k
by (induction n) (simp_all add: fds_deriv_def fds_eq_iff fds_nth_fds' scaleR_conv_of_real)
thus ?thesis by (intro fds_eqI) simp_all
qed
have deriv': "(λn. eval_fds ((fds_deriv ^^ n) f) (complex_of_real a)) =
(λn. (- 1) ^ n * complex_of_real (∑⇩ak. fds_nth f' k * ln (real k) ^ n / real k powr a))"
proof
fix n
have "eval_fds ((fds_deriv ^^ n) f) (of_real a) =
(∑⇩ak. fds_nth ((fds_deriv ^^ n) f) k / of_nat k powr complex_of_real a)"
using nth_deriv_conv by (subst eval_fds_altdef) auto
hence "eval_fds ((fds_deriv ^^ n) f) (of_real a) =
(∑⇩ak. (- 1) ^ n *⇩R (fds_nth f k * ln (real k) ^ n / k powr a))"
by (simp add: nth_deriv_eq fds_nth_fds' powr_Reals_eq scaleR_conv_of_real algebra_simps)
also have "… = (- 1) ^ n * (∑⇩ak. of_real (fds_nth f' k * ln (real k) ^ n / k powr a))"
by (subst infsetsum_scaleR_right) (simp_all add: scaleR_conv_of_real f_f')
also have "… = (- 1) ^ n * of_real (∑⇩ak. fds_nth f' k * ln (real k) ^ n / k powr a)"
by (subst infsetsum_of_real) (rule refl)
finally show "eval_fds ((fds_deriv ^^ n) f) (complex_of_real a) =
(- 1) ^ n * complex_of_real (∑⇩ak. fds_nth f' k * ln (real k) ^ n / real k powr a)" .
qed
define s :: complex where "s = c - ε / 2"
have s: "Re s < c" using assms δ by (simp_all add: s_def ε_def field_simps)
have "s ∈ ball a (1 + ε)" using s by (simp add: a_def dist_norm cmod_def s_def)
from holomorphic_power_series[OF holo this]
have sums: "(λn. (deriv ^^ n) g' a / fact n * (s - a) ^ n) sums g' s" by simp
also note deriv
also have "s - a = -of_real (1 + ε / 2)" by (simp add: s_def a_def)
also have "(λn. … ^ n) = (λn. of_real ((-1) ^ n * (1 + ε / 2) ^ n))"
by (intro ext) (subst power_minus, auto)
also have "(λn. eval_fds ((fds_deriv ^^ n) f) a / fact n * … n) =
(λn. of_real ((-1) ^ n * eval_fds ((fds_deriv ^^ n) f') a / fact n * (1+ε/2) ^ n))"
using nth_deriv_conv by (simp add: f_f' fds_abs_converges_imp_converges mult_ac)
finally have "summable …" by (simp add: sums_iff)
hence summable: "summable (λn. (-1)^n * eval_fds ((fds_deriv ^^ n) f') a / fact n * (1+ε/2)^n)"
by (subst (asm) summable_of_real_iff)
have "(λ(n,k). (-1)^n * fds_nth f k * ln (real k) ^ n / (real k powr a) * ((s-a) ^ n / fact n))
abs_summable_on (UNIV × UNIV)"
proof (subst abs_summable_on_Sigma_iff, safe, goal_cases)
case (3 n)
from nth_deriv_conv[of n] show ?case
unfolding fds_abs_converges_altdef'
by (intro abs_summable_on_cmult_left) (simp add: nth_deriv_eq fds_nth_fds' powr_Reals_eq)
next
case 4
have nth_deriv_f_f': "(fds_deriv ^^ n) f = fds_of_real ((fds_deriv ^^ n) f')" for n
by (induction n) (auto simp: f'_def fds_of_real_norm)
have norm_nth_deriv_f: "norm (fds_nth ((fds_deriv ^^ n) f) k) =
(-1) ^ n * of_real (fds_nth ((fds_deriv ^^ n) f') k)" for n k
proof (induction n)
case (Suc n)
thus ?case by (cases k) (auto simp: f_f' fds_nth_deriv scaleR_conv_of_real norm_mult)
qed (auto simp: f'_nonneg f_f')
note summable
also have "(λn. (-1)^n * eval_fds ((fds_deriv ^^ n) f') a / fact n * (1+ε/2)^n) =
(λn. ∑⇩ak. norm ((- 1) ^ n * fds_nth f k * ln (real k) ^ n /
(real k powr a) * ((s - a) ^ n / fact n)))" (is "_ = ?h")
proof (rule ext, goal_cases)
case (1 n)
have "(∑⇩ak. norm ((- 1) ^ n * fds_nth f k * ln (real k) ^ n /
(real k powr a) * ((s - a) ^ n / fact n))) =
(norm ((s - a) ^ n / fact n) * (-1) ^ n) *⇩R
(∑⇩ak. (-1) ^ n * norm (fds_nth ((fds_deriv ^^ n) f) k / real k powr a))" (is "_ = _ *⇩R ?S")
by (subst infsetsum_scaleR_right [symmetric])
(auto simp: norm_mult norm_divide norm_power mult_ac nth_deriv_eq fds_nth_fds')
also have "?S = (∑⇩ak. fds_nth ((fds_deriv ^^ n) f') k / real k powr a)"
by (intro infsetsum_cong) (auto simp: norm_mult norm_divide norm_power norm_nth_deriv_f)
also have "… = eval_fds ((fds_deriv ^^ n) f') a"
using nth_deriv_conv[of n] by (subst eval_fds_altdef) (auto simp: f'_def nth_deriv_f_f')
also have "(norm ((s - a) ^ n / fact n) * (- 1) ^ n) *⇩R eval_fds ((fds_deriv ^^ n) f') a =
(-1) ^ n * eval_fds ((fds_deriv ^^ n) f') a / fact n * norm (s - a) ^ n"
by (simp add: norm_divide norm_power)
also have s_a: "s - a = -of_real (1 + ε / 2)" by (simp add: s_def a_def)
have "norm (s - a) = 1 + ε / 2" unfolding s_a norm_minus_cancel norm_of_real using ε by simp
finally show ?case ..
qed
also have "?h n ≥ 0" for n by (intro infsetsum_nonneg) auto
hence "?h = (λn. norm (?h n))" by simp
finally show ?case unfolding abs_summable_on_nat_iff' .
qed auto
hence "(λ(k,n). (-1)^n * fds_nth f k * ln (real k) ^ n / (real k powr a) * ((s-a) ^ n / fact n))
abs_summable_on (UNIV × UNIV)"
by (subst (asm) abs_summable_on_Times_swap) (simp add: case_prod_unfold)
hence "(λk. ∑⇩an. (- 1) ^ n * fds_nth f k * ln (real k) ^ n / (k powr a) *
((s - a) ^ n / fact n)) abs_summable_on UNIV" (is "?h abs_summable_on _")
by (rule abs_summable_on_Sigma_project1') auto
also have "?this ⟷ (λk. fds_nth f k / nat_power k s) abs_summable_on UNIV"
proof (intro abs_summable_on_cong refl, goal_cases)
case (1 k)
have "?h k = (fds_nth f' k / k powr a) *⇩R (∑⇩an. (-ln (real k) * (s - a)) ^ n / fact n)"
by (subst infsetsum_scaleR_right [symmetric], rule infsetsum_cong)
(simp_all add: scaleR_conv_of_real f_f' power_minus' power_mult_distrib divide_simps)
also have "(∑⇩an. (-ln (real k) * (s - a)) ^ n / fact n) = exp (-ln (real k) * (s - a))"
using exp_converges[of "-ln k * (s - a)"] exp_converges[of "norm (-ln k * (s - a))"]
by (subst infsetsum_nat') (auto simp: abs_summable_on_nat_iff' sums_iff scaleR_conv_of_real
divide_simps norm_divide norm_mult norm_power)
also have "(fds_nth f' k / k powr a) *⇩R … = fds_nth f k / nat_power k s"
by (auto simp: scaleR_conv_of_real f_f' powr_def exp_minus
field_simps exp_of_real [symmetric] exp_diff)
finally show ?case .
qed
finally have "fds_abs_converges f s"
by (simp add: fds_abs_converges_def abs_summable_on_nat_iff')
thus ?thesis by (intro exI[of _ "(c - ε / 2)"]) (auto simp: s_def a_def ε)
qed
theorem pringsheim_landau:
fixes c :: real and f :: "complex fds"
assumes "nonneg_dirichlet_series f"
assumes abscissa: "abs_conv_abscissa f = c"
assumes g: "⋀s. s ∈ A ⟹ Re s > c ⟹ g s = eval_fds f s"
assumes "g holomorphic_on A" "open A" "c ∈ A"
shows False
proof -
have "∃x<c. fds_abs_converges f (complex_of_real x)"
by (rule pringsheim_landau_aux[where g = g and A = A]) (insert assms, auto)
then obtain x where x: "x < c" "fds_abs_converges f (complex_of_real x)" by blast
hence "abs_conv_abscissa f ≤ complex_of_real x ∙ 1"
unfolding abs_conv_abscissa_def
by (intro Inf_lower) (auto simp: image_iff intro!: exI[of _ "of_real x"])
also have "… < abs_conv_abscissa f" using assms x by simp
finally show False by simp
qed
corollary entire_continuation_imp_abs_conv_abscissa_MInfty:
assumes "nonneg_dirichlet_series f"
assumes c: "c ≥ abs_conv_abscissa f"
assumes g: "⋀s. Re s > c ⟹ g s = eval_fds f s"
assumes holo: "g holomorphic_on UNIV"
shows "abs_conv_abscissa f = -∞"
proof (rule ccontr)
assume "abs_conv_abscissa f ≠ -∞"
with c obtain a where abscissa [simp]: "abs_conv_abscissa f = ereal a"
by (cases "abs_conv_abscissa f") auto
show False
proof (rule pringsheim_landau[OF assms(1) abscissa _ holo])
fix s assume s: "Re s > a"
show "g s = eval_fds f s"
proof (rule sym, rule analytic_continuation_open[of _ _ _ g])
show "g holomorphic_on {s. Re s > a}" by (rule holomorphic_on_subset[OF holo]) auto
from assms show "{s. Re s > c} ⊆ {s. Re s > a}" by auto
next
have "conv_abscissa f ≤ abs_conv_abscissa f" by (rule conv_le_abs_conv_abscissa)
also have "… = ereal a" by simp
finally show "eval_fds f holomorphic_on {s. Re s > a}"
by (intro holomorphic_intros) (auto intro: le_less_trans)
qed (insert assms s, auto intro!: exI[of _ "of_real (c + 1)"]
open_halfspace_Re_gt convex_connected convex_halfspace_Re_gt)
qed auto
qed
subsection ‹Convergence of the $\zeta$ and M\"{o}bius $\mu$ series›
lemma fds_abs_summable_zeta_real_iff [simp]:
"fds_abs_converges fds_zeta s ⟷ s > (1 :: real)"
proof -
have "fds_abs_converges fds_zeta s ⟷ summable (λn. real n powr -s)"
unfolding fds_abs_converges_def
by (intro summable_cong always_eventually)
(auto simp: fds_nth_zeta powr_minus divide_simps)
also have "… ⟷ s > 1" by (simp add: summable_real_powr_iff)
finally show ?thesis .
qed
lemma fds_abs_summable_zeta_real: "s > (1 :: real) ⟹ fds_abs_converges fds_zeta s"
by simp
lemma fds_abs_converges_moebius_mu_real:
assumes "s > (1 :: real)"
shows "fds_abs_converges (fds moebius_mu) s"
unfolding fds_abs_converges_def
proof (rule summable_comparison_test, intro exI allI impI)
fix n :: nat
show "norm (norm (fds_nth (fds moebius_mu) n / nat_power n s)) ≤ n powr (-s)"
by (simp add: powr_minus divide_simps abs_moebius_mu_le)
next
from assms show "summable (λn. real n powr -s)" by (simp add: summable_real_powr_iff)
qed
subsection ‹Application to the M\"{o}bius $\mu$ function›
lemma inverse_squares_sums': "(λn. 1 / real n ^ 2) sums (pi ^ 2 / 6)"
using inverse_squares_sums sums_Suc_iff[of "λn. 1 / real n ^ 2" "pi^2 / 6"] by simp
lemma norm_summable_moebius_over_square:
"summable (λn. norm (moebius_mu n / real n ^ 2))"
proof (subst summable_Suc_iff [symmetric], rule summable_comparison_test)
show "summable (λn. 1 / real (Suc n) ^ 2)"
using inverse_squares_sums by (simp add: sums_iff)
qed (auto simp del: of_nat_Suc simp: field_simps abs_moebius_mu_le)
lemma summable_moebius_over_square:
"summable (λn. moebius_mu n / real n ^ 2)"
using norm_summable_moebius_over_square by (rule summable_norm_cancel)
lemma moebius_over_square_sums: "(λn. moebius_mu n / n⇧2) sums (6 / pi⇧2)"
proof -
have "1 = eval_fds (1 :: real fds) 2" by simp
also have "(1 :: real fds) = fds_zeta * fds moebius_mu"
by (rule fds_zeta_times_moebius_mu [symmetric])
also have "eval_fds … 2 = eval_fds fds_zeta 2 * eval_fds (fds moebius_mu) 2"
by (intro eval_fds_mult fds_abs_converges_moebius_mu_real) simp_all
also have "… = pi ^ 2 / 6 * (∑n. moebius_mu n / (real n)⇧2)"
using inverse_squares_sums' by (simp add: eval_fds_at_numeral suminf_fds_zeta_aux sums_iff)
finally have "(∑n. moebius_mu n / (real n)⇧2) = 6 / pi ^ 2" by (simp add: field_simps)
with summable_moebius_over_square show ?thesis by (simp add: sums_iff)
qed
end