Analytical solution of an infinite series

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Discussion Overview

The discussion revolves around finding an analytical solution for an infinite series represented by Ʃ_{n=1}^{\infty} (β^{n-1}y^{R^{n}}e^{A(1-R^{2n})}), with specific constraints on the parameters β, R, y, and A. Participants explore methods for approximating the series analytically, including references to known mathematical functions and series.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant seeks an analytical approximation for the infinite series, noting its convergence by the Ratio test.
  • Another participant suggests exploring Taylor series or differential equation series, such as Hypergeometric or Bessel functions, to find a similar form.
  • A request for references on approximating series using the suggested methods is made by the original poster.
  • A further exploration of simplifying the series while retaining the lacunary term is proposed, with a specific example using β=1/2, R=1/2, and A=1 to illustrate the approach.
  • Participants discuss the possibility of finding a non-trivial series that can yield an analytic expression involving special functions like Bessel, Erf, hypergeometric, or Lambert W functions.

Areas of Agreement / Disagreement

Participants express uncertainty about how to approach the series analytically, and there is no consensus on a specific method or solution. Multiple viewpoints on potential approaches remain present.

Contextual Notes

Participants acknowledge the complexity of the series and the need for simplification, but there are unresolved aspects regarding the applicability of the suggested methods and the specific forms of the series that could yield analytic expressions.

Matheco
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How to find the value of an infinite series. for e.g.[itex]Ʃ_{n=1}^{\infty} (β^{n-1}y^{R^{n}}e^{A(1-R^{2n})})[/itex]

where β<1, R<1, y>1, and A>0?

Note that this series is covergent by Ratio test. I already have the numerical solution of the above. However, I am interested in analytical solution (approximation) of the value of infinite series (in terms of β,R, y, A).
 
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Hey Matheco and welcome to the forums.

One suggestion I have is to see if you can find a taylor series or DE series (like the Hypergeometric or Bessel functions) and see if you can get a form that is similar.

Google should give you some results for tables of series in mathematics somewhere.

Other than that, you might try looking at the structure of the differential equations and integrals and see if you can construct a DE system that matches your equation.

Depending on how badly you want to solve it, it could be an interesting research problem.
 
Thanks chiro for your reply. At the moment I am clueless about how to deal with this series. Could you recommend a reference where series are approximated by methods suggested by you?
 
Matheco said:
At the moment I am clueless about how to deal with this series.

Just one. That's all I'd be interested in at this point. That is, can I find just one series that I can compute it's analytic expression?

The term [itex]y^{R^n}[/itex] is indicative of a lacunary function:

http://en.wikipedia.org/wiki/Lacunary_function

So we have a start. How much can we simplify your series, keep the lacunary term, and find an analytic expression for the resulting series?

How about we let [itex]\beta=1/2, R=1/2, A=1[/itex]

Then we get:

[tex]\sum_{n=1}^{\infty} \frac{1}{2^{n-1}} y^{\frac{1}{2^n}}e^{(1-\frac{1}{4^n})}[/tex]

Can we find an analytic expression for that one? If not, then can we come up with another set of non-trivial values of the parameters and find the analytic expression for the resulting series? Suppose that was your goal: find just one non-trivial series that you can compute any kind of analytic expression for including an analytic expression containing special functions like Bessel, Erf, hypergeometric, Lambert W, or other functions.

Could you do that?
 

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