Extracting Dirichlet series coefficientsDirichlet series expansion of an analytic functionIs the maximum...



Extracting Dirichlet series coefficients


Dirichlet series expansion of an analytic functionIs the maximum domain to which a Dirichlet series can be continued always a halfplane?Dirichlet series expansion of an analytic functionMultiplicative functions whose Dirichlet series have essential singularitiesWhat is known about the polynomial factorization of power series?Smoothing Dirichlet Series partial sums by means of Pontifex Path Bending FunctionsDirichlet series decomposition of arbitrary functionFormal theory of (some) generating functions in $t$ and $t^{-1}$?Reaching Hecke eigenvalues from a trace formulaAsymptotic growth of the of Taylor coefficients of the inverse of a functionDirichlet series associated with polynomials













5












$begingroup$


Cauchy's integral formula is a powerful method to extract the $n$'th power series coefficient of an analytic function by evaluating a single complex integral. Is there any such analytic method to extract (ordinary) Dirichlet series coefficients? That is, assuming that a given function $f(s)$ admits a Dirichlet series expansion $$sum_n a_n n^{-s},$$ is there any known method to compute a desired coefficient $a_n$?










share|cite|improve this question









$endgroup$








  • 2




    $begingroup$
    Otherwise you can find the $a_n$ one by one from the asymptotic as $s to +infty$. I wonder if there is an analog of $c_n = frac{F^{(n)}(0)}{n!} = lim_{z to 0} frac{sum_{k=0}^n {k choose n} (-1)^{k-n} F(nz)}{z^n n!}$
    $endgroup$
    – reuns
    2 days ago












  • $begingroup$
    Possibly relevant: mathoverflow.net/questions/30975/…
    $endgroup$
    – M.G.
    yesterday
















5












$begingroup$


Cauchy's integral formula is a powerful method to extract the $n$'th power series coefficient of an analytic function by evaluating a single complex integral. Is there any such analytic method to extract (ordinary) Dirichlet series coefficients? That is, assuming that a given function $f(s)$ admits a Dirichlet series expansion $$sum_n a_n n^{-s},$$ is there any known method to compute a desired coefficient $a_n$?










share|cite|improve this question









$endgroup$








  • 2




    $begingroup$
    Otherwise you can find the $a_n$ one by one from the asymptotic as $s to +infty$. I wonder if there is an analog of $c_n = frac{F^{(n)}(0)}{n!} = lim_{z to 0} frac{sum_{k=0}^n {k choose n} (-1)^{k-n} F(nz)}{z^n n!}$
    $endgroup$
    – reuns
    2 days ago












  • $begingroup$
    Possibly relevant: mathoverflow.net/questions/30975/…
    $endgroup$
    – M.G.
    yesterday














5












5








5


2



$begingroup$


Cauchy's integral formula is a powerful method to extract the $n$'th power series coefficient of an analytic function by evaluating a single complex integral. Is there any such analytic method to extract (ordinary) Dirichlet series coefficients? That is, assuming that a given function $f(s)$ admits a Dirichlet series expansion $$sum_n a_n n^{-s},$$ is there any known method to compute a desired coefficient $a_n$?










share|cite|improve this question









$endgroup$




Cauchy's integral formula is a powerful method to extract the $n$'th power series coefficient of an analytic function by evaluating a single complex integral. Is there any such analytic method to extract (ordinary) Dirichlet series coefficients? That is, assuming that a given function $f(s)$ admits a Dirichlet series expansion $$sum_n a_n n^{-s},$$ is there any known method to compute a desired coefficient $a_n$?







analytic-number-theory power-series dirichlet-series






share|cite|improve this question













share|cite|improve this question











share|cite|improve this question




share|cite|improve this question










asked 2 days ago









MCHMCH

32019




32019








  • 2




    $begingroup$
    Otherwise you can find the $a_n$ one by one from the asymptotic as $s to +infty$. I wonder if there is an analog of $c_n = frac{F^{(n)}(0)}{n!} = lim_{z to 0} frac{sum_{k=0}^n {k choose n} (-1)^{k-n} F(nz)}{z^n n!}$
    $endgroup$
    – reuns
    2 days ago












  • $begingroup$
    Possibly relevant: mathoverflow.net/questions/30975/…
    $endgroup$
    – M.G.
    yesterday














  • 2




    $begingroup$
    Otherwise you can find the $a_n$ one by one from the asymptotic as $s to +infty$. I wonder if there is an analog of $c_n = frac{F^{(n)}(0)}{n!} = lim_{z to 0} frac{sum_{k=0}^n {k choose n} (-1)^{k-n} F(nz)}{z^n n!}$
    $endgroup$
    – reuns
    2 days ago












  • $begingroup$
    Possibly relevant: mathoverflow.net/questions/30975/…
    $endgroup$
    – M.G.
    yesterday








2




2




$begingroup$
Otherwise you can find the $a_n$ one by one from the asymptotic as $s to +infty$. I wonder if there is an analog of $c_n = frac{F^{(n)}(0)}{n!} = lim_{z to 0} frac{sum_{k=0}^n {k choose n} (-1)^{k-n} F(nz)}{z^n n!}$
$endgroup$
– reuns
2 days ago






$begingroup$
Otherwise you can find the $a_n$ one by one from the asymptotic as $s to +infty$. I wonder if there is an analog of $c_n = frac{F^{(n)}(0)}{n!} = lim_{z to 0} frac{sum_{k=0}^n {k choose n} (-1)^{k-n} F(nz)}{z^n n!}$
$endgroup$
– reuns
2 days ago














$begingroup$
Possibly relevant: mathoverflow.net/questions/30975/…
$endgroup$
– M.G.
yesterday




$begingroup$
Possibly relevant: mathoverflow.net/questions/30975/…
$endgroup$
– M.G.
yesterday










2 Answers
2






active

oldest

votes


















7












$begingroup$

Even for more general Dirichlet series
$$f(z)=sum_{0}^infty a_n e^{-lambda_nz}$$
there is the formula
$$a_ne^{-lambda_nsigma}=lim_{Ttoinfty}frac{1}{T}int_{t_0}^Tf(sigma+it)e^{lambda_n it}dt,$$
where $t_0$ is arbitrary (real) and $sigma>sigma_u$, the abscissa of uniform convergence.



This formula determines both $lambda_n$ and $a_n$: the RHS=0 when we integrate against $e^{ilambda t}$ with $lambdaneq lambda_n$.
The class of functions which can be represented by such a series is called (analytic) almost periodic functions (on a vertical line ${s=sigma+it:tin R}$). The "number-theoretic case" corresponds to $lambda_n=n$.



Ref. S. Mandelbrojt, Series de Dirichlet, Paris, Gauthier-Villars, 1969.
Dirichlet series with complex $lambda_n$ have been also studied (by A. F. Leont'ev and his school).






share|cite|improve this answer











$endgroup$













  • $begingroup$
    If we don't know the $lambda_n$ coefficients, is there a way to obtain them as well, or the problem becomes way too undetermined?
    $endgroup$
    – M.G.
    yesterday










  • $begingroup$
    @M.G. Number-theoretic case is $lambda_n=log n$. In general, they are determined by the same formula I wrote: apply it with arbitrary $lambda$, the RHS will be $0$ for all $lambda$ except countably many $lambda_n$. For the discussion of the class of functions $f$ which admit such a representation, see the book of Mandelbrojt that I mentioned.
    $endgroup$
    – Alexandre Eremenko
    yesterday





















7












$begingroup$

Yes. If $f(s)$ has a finite abscissa of absolute convergence $sigma_a$, then $forall sigma > sigma_a$:
$$
lim_{Ttoinfty} frac{1}{2T} int_{-T}^{T} f(sigma+ it)n^{it} mathrm{d}t = frac{a_n}{n^{sigma}}.
$$

IIRC, the proof can be found in Apostol's book on Analytic Number Theory.






share|cite|improve this answer









$endgroup$









  • 1




    $begingroup$
    I think it holds for $sigma > sigma_c$ the absicssa of simple convergence because $f(s) = (s-s_0)int_1^infty (sum_{m le x} a_m m^{-s_0}) x^{-s+s_0-1}dx = O(s)$ so we can replace $f(sigma+it)$ by $f(sigma+i.) ast frac{ k}{sqrt{2pi}} e^{-t^2 k^2/2} = sum_m a_m m^{-sigma-it} e^{- frac{ln^2m}{2 k^2}}$ to make it absolutely convergent
    $endgroup$
    – reuns
    2 days ago












Your Answer








StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "504"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});


}
});














draft saved

draft discarded


















StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmathoverflow.net%2fquestions%2f329980%2fextracting-dirichlet-series-coefficients%23new-answer', 'question_page');
}
);

Post as a guest















Required, but never shown

























2 Answers
2






active

oldest

votes








2 Answers
2






active

oldest

votes









active

oldest

votes






active

oldest

votes









7












$begingroup$

Even for more general Dirichlet series
$$f(z)=sum_{0}^infty a_n e^{-lambda_nz}$$
there is the formula
$$a_ne^{-lambda_nsigma}=lim_{Ttoinfty}frac{1}{T}int_{t_0}^Tf(sigma+it)e^{lambda_n it}dt,$$
where $t_0$ is arbitrary (real) and $sigma>sigma_u$, the abscissa of uniform convergence.



This formula determines both $lambda_n$ and $a_n$: the RHS=0 when we integrate against $e^{ilambda t}$ with $lambdaneq lambda_n$.
The class of functions which can be represented by such a series is called (analytic) almost periodic functions (on a vertical line ${s=sigma+it:tin R}$). The "number-theoretic case" corresponds to $lambda_n=n$.



Ref. S. Mandelbrojt, Series de Dirichlet, Paris, Gauthier-Villars, 1969.
Dirichlet series with complex $lambda_n$ have been also studied (by A. F. Leont'ev and his school).






share|cite|improve this answer











$endgroup$













  • $begingroup$
    If we don't know the $lambda_n$ coefficients, is there a way to obtain them as well, or the problem becomes way too undetermined?
    $endgroup$
    – M.G.
    yesterday










  • $begingroup$
    @M.G. Number-theoretic case is $lambda_n=log n$. In general, they are determined by the same formula I wrote: apply it with arbitrary $lambda$, the RHS will be $0$ for all $lambda$ except countably many $lambda_n$. For the discussion of the class of functions $f$ which admit such a representation, see the book of Mandelbrojt that I mentioned.
    $endgroup$
    – Alexandre Eremenko
    yesterday


















7












$begingroup$

Even for more general Dirichlet series
$$f(z)=sum_{0}^infty a_n e^{-lambda_nz}$$
there is the formula
$$a_ne^{-lambda_nsigma}=lim_{Ttoinfty}frac{1}{T}int_{t_0}^Tf(sigma+it)e^{lambda_n it}dt,$$
where $t_0$ is arbitrary (real) and $sigma>sigma_u$, the abscissa of uniform convergence.



This formula determines both $lambda_n$ and $a_n$: the RHS=0 when we integrate against $e^{ilambda t}$ with $lambdaneq lambda_n$.
The class of functions which can be represented by such a series is called (analytic) almost periodic functions (on a vertical line ${s=sigma+it:tin R}$). The "number-theoretic case" corresponds to $lambda_n=n$.



Ref. S. Mandelbrojt, Series de Dirichlet, Paris, Gauthier-Villars, 1969.
Dirichlet series with complex $lambda_n$ have been also studied (by A. F. Leont'ev and his school).






share|cite|improve this answer











$endgroup$













  • $begingroup$
    If we don't know the $lambda_n$ coefficients, is there a way to obtain them as well, or the problem becomes way too undetermined?
    $endgroup$
    – M.G.
    yesterday










  • $begingroup$
    @M.G. Number-theoretic case is $lambda_n=log n$. In general, they are determined by the same formula I wrote: apply it with arbitrary $lambda$, the RHS will be $0$ for all $lambda$ except countably many $lambda_n$. For the discussion of the class of functions $f$ which admit such a representation, see the book of Mandelbrojt that I mentioned.
    $endgroup$
    – Alexandre Eremenko
    yesterday
















7












7








7





$begingroup$

Even for more general Dirichlet series
$$f(z)=sum_{0}^infty a_n e^{-lambda_nz}$$
there is the formula
$$a_ne^{-lambda_nsigma}=lim_{Ttoinfty}frac{1}{T}int_{t_0}^Tf(sigma+it)e^{lambda_n it}dt,$$
where $t_0$ is arbitrary (real) and $sigma>sigma_u$, the abscissa of uniform convergence.



This formula determines both $lambda_n$ and $a_n$: the RHS=0 when we integrate against $e^{ilambda t}$ with $lambdaneq lambda_n$.
The class of functions which can be represented by such a series is called (analytic) almost periodic functions (on a vertical line ${s=sigma+it:tin R}$). The "number-theoretic case" corresponds to $lambda_n=n$.



Ref. S. Mandelbrojt, Series de Dirichlet, Paris, Gauthier-Villars, 1969.
Dirichlet series with complex $lambda_n$ have been also studied (by A. F. Leont'ev and his school).






share|cite|improve this answer











$endgroup$



Even for more general Dirichlet series
$$f(z)=sum_{0}^infty a_n e^{-lambda_nz}$$
there is the formula
$$a_ne^{-lambda_nsigma}=lim_{Ttoinfty}frac{1}{T}int_{t_0}^Tf(sigma+it)e^{lambda_n it}dt,$$
where $t_0$ is arbitrary (real) and $sigma>sigma_u$, the abscissa of uniform convergence.



This formula determines both $lambda_n$ and $a_n$: the RHS=0 when we integrate against $e^{ilambda t}$ with $lambdaneq lambda_n$.
The class of functions which can be represented by such a series is called (analytic) almost periodic functions (on a vertical line ${s=sigma+it:tin R}$). The "number-theoretic case" corresponds to $lambda_n=n$.



Ref. S. Mandelbrojt, Series de Dirichlet, Paris, Gauthier-Villars, 1969.
Dirichlet series with complex $lambda_n$ have been also studied (by A. F. Leont'ev and his school).







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








edited yesterday

























answered 2 days ago









Alexandre EremenkoAlexandre Eremenko

52k6146265




52k6146265












  • $begingroup$
    If we don't know the $lambda_n$ coefficients, is there a way to obtain them as well, or the problem becomes way too undetermined?
    $endgroup$
    – M.G.
    yesterday










  • $begingroup$
    @M.G. Number-theoretic case is $lambda_n=log n$. In general, they are determined by the same formula I wrote: apply it with arbitrary $lambda$, the RHS will be $0$ for all $lambda$ except countably many $lambda_n$. For the discussion of the class of functions $f$ which admit such a representation, see the book of Mandelbrojt that I mentioned.
    $endgroup$
    – Alexandre Eremenko
    yesterday




















  • $begingroup$
    If we don't know the $lambda_n$ coefficients, is there a way to obtain them as well, or the problem becomes way too undetermined?
    $endgroup$
    – M.G.
    yesterday










  • $begingroup$
    @M.G. Number-theoretic case is $lambda_n=log n$. In general, they are determined by the same formula I wrote: apply it with arbitrary $lambda$, the RHS will be $0$ for all $lambda$ except countably many $lambda_n$. For the discussion of the class of functions $f$ which admit such a representation, see the book of Mandelbrojt that I mentioned.
    $endgroup$
    – Alexandre Eremenko
    yesterday


















$begingroup$
If we don't know the $lambda_n$ coefficients, is there a way to obtain them as well, or the problem becomes way too undetermined?
$endgroup$
– M.G.
yesterday




$begingroup$
If we don't know the $lambda_n$ coefficients, is there a way to obtain them as well, or the problem becomes way too undetermined?
$endgroup$
– M.G.
yesterday












$begingroup$
@M.G. Number-theoretic case is $lambda_n=log n$. In general, they are determined by the same formula I wrote: apply it with arbitrary $lambda$, the RHS will be $0$ for all $lambda$ except countably many $lambda_n$. For the discussion of the class of functions $f$ which admit such a representation, see the book of Mandelbrojt that I mentioned.
$endgroup$
– Alexandre Eremenko
yesterday






$begingroup$
@M.G. Number-theoretic case is $lambda_n=log n$. In general, they are determined by the same formula I wrote: apply it with arbitrary $lambda$, the RHS will be $0$ for all $lambda$ except countably many $lambda_n$. For the discussion of the class of functions $f$ which admit such a representation, see the book of Mandelbrojt that I mentioned.
$endgroup$
– Alexandre Eremenko
yesterday













7












$begingroup$

Yes. If $f(s)$ has a finite abscissa of absolute convergence $sigma_a$, then $forall sigma > sigma_a$:
$$
lim_{Ttoinfty} frac{1}{2T} int_{-T}^{T} f(sigma+ it)n^{it} mathrm{d}t = frac{a_n}{n^{sigma}}.
$$

IIRC, the proof can be found in Apostol's book on Analytic Number Theory.






share|cite|improve this answer









$endgroup$









  • 1




    $begingroup$
    I think it holds for $sigma > sigma_c$ the absicssa of simple convergence because $f(s) = (s-s_0)int_1^infty (sum_{m le x} a_m m^{-s_0}) x^{-s+s_0-1}dx = O(s)$ so we can replace $f(sigma+it)$ by $f(sigma+i.) ast frac{ k}{sqrt{2pi}} e^{-t^2 k^2/2} = sum_m a_m m^{-sigma-it} e^{- frac{ln^2m}{2 k^2}}$ to make it absolutely convergent
    $endgroup$
    – reuns
    2 days ago
















7












$begingroup$

Yes. If $f(s)$ has a finite abscissa of absolute convergence $sigma_a$, then $forall sigma > sigma_a$:
$$
lim_{Ttoinfty} frac{1}{2T} int_{-T}^{T} f(sigma+ it)n^{it} mathrm{d}t = frac{a_n}{n^{sigma}}.
$$

IIRC, the proof can be found in Apostol's book on Analytic Number Theory.






share|cite|improve this answer









$endgroup$









  • 1




    $begingroup$
    I think it holds for $sigma > sigma_c$ the absicssa of simple convergence because $f(s) = (s-s_0)int_1^infty (sum_{m le x} a_m m^{-s_0}) x^{-s+s_0-1}dx = O(s)$ so we can replace $f(sigma+it)$ by $f(sigma+i.) ast frac{ k}{sqrt{2pi}} e^{-t^2 k^2/2} = sum_m a_m m^{-sigma-it} e^{- frac{ln^2m}{2 k^2}}$ to make it absolutely convergent
    $endgroup$
    – reuns
    2 days ago














7












7








7





$begingroup$

Yes. If $f(s)$ has a finite abscissa of absolute convergence $sigma_a$, then $forall sigma > sigma_a$:
$$
lim_{Ttoinfty} frac{1}{2T} int_{-T}^{T} f(sigma+ it)n^{it} mathrm{d}t = frac{a_n}{n^{sigma}}.
$$

IIRC, the proof can be found in Apostol's book on Analytic Number Theory.






share|cite|improve this answer









$endgroup$



Yes. If $f(s)$ has a finite abscissa of absolute convergence $sigma_a$, then $forall sigma > sigma_a$:
$$
lim_{Ttoinfty} frac{1}{2T} int_{-T}^{T} f(sigma+ it)n^{it} mathrm{d}t = frac{a_n}{n^{sigma}}.
$$

IIRC, the proof can be found in Apostol's book on Analytic Number Theory.







share|cite|improve this answer












share|cite|improve this answer



share|cite|improve this answer










answered 2 days ago









M.G.M.G.

3,04022740




3,04022740








  • 1




    $begingroup$
    I think it holds for $sigma > sigma_c$ the absicssa of simple convergence because $f(s) = (s-s_0)int_1^infty (sum_{m le x} a_m m^{-s_0}) x^{-s+s_0-1}dx = O(s)$ so we can replace $f(sigma+it)$ by $f(sigma+i.) ast frac{ k}{sqrt{2pi}} e^{-t^2 k^2/2} = sum_m a_m m^{-sigma-it} e^{- frac{ln^2m}{2 k^2}}$ to make it absolutely convergent
    $endgroup$
    – reuns
    2 days ago














  • 1




    $begingroup$
    I think it holds for $sigma > sigma_c$ the absicssa of simple convergence because $f(s) = (s-s_0)int_1^infty (sum_{m le x} a_m m^{-s_0}) x^{-s+s_0-1}dx = O(s)$ so we can replace $f(sigma+it)$ by $f(sigma+i.) ast frac{ k}{sqrt{2pi}} e^{-t^2 k^2/2} = sum_m a_m m^{-sigma-it} e^{- frac{ln^2m}{2 k^2}}$ to make it absolutely convergent
    $endgroup$
    – reuns
    2 days ago








1




1




$begingroup$
I think it holds for $sigma > sigma_c$ the absicssa of simple convergence because $f(s) = (s-s_0)int_1^infty (sum_{m le x} a_m m^{-s_0}) x^{-s+s_0-1}dx = O(s)$ so we can replace $f(sigma+it)$ by $f(sigma+i.) ast frac{ k}{sqrt{2pi}} e^{-t^2 k^2/2} = sum_m a_m m^{-sigma-it} e^{- frac{ln^2m}{2 k^2}}$ to make it absolutely convergent
$endgroup$
– reuns
2 days ago




$begingroup$
I think it holds for $sigma > sigma_c$ the absicssa of simple convergence because $f(s) = (s-s_0)int_1^infty (sum_{m le x} a_m m^{-s_0}) x^{-s+s_0-1}dx = O(s)$ so we can replace $f(sigma+it)$ by $f(sigma+i.) ast frac{ k}{sqrt{2pi}} e^{-t^2 k^2/2} = sum_m a_m m^{-sigma-it} e^{- frac{ln^2m}{2 k^2}}$ to make it absolutely convergent
$endgroup$
– reuns
2 days ago


















draft saved

draft discarded




















































Thanks for contributing an answer to MathOverflow!


  • Please be sure to answer the question. Provide details and share your research!

But avoid



  • Asking for help, clarification, or responding to other answers.

  • Making statements based on opinion; back them up with references or personal experience.


Use MathJax to format equations. MathJax reference.


To learn more, see our tips on writing great answers.




draft saved


draft discarded














StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmathoverflow.net%2fquestions%2f329980%2fextracting-dirichlet-series-coefficients%23new-answer', 'question_page');
}
);

Post as a guest















Required, but never shown





















































Required, but never shown














Required, but never shown












Required, but never shown







Required, but never shown

































Required, but never shown














Required, but never shown












Required, but never shown







Required, but never shown







Popular posts from this blog

Why not use the yoke to control yaw, as well as pitch and roll? Announcing the arrival of...

Couldn't open a raw socket. Error: Permission denied (13) (nmap)Is it possible to run networking commands...

VNC viewer RFB protocol error: bad desktop size 0x0I Cannot Type the Key 'd' (lowercase) in VNC Viewer...