Is f(x) Representable as a Special Function?

  • Context: Graduate 
  • Thread starter Thread starter pierce15
  • Start date Start date
  • Tags Tags
    Function Series
Click For Summary

Discussion Overview

The discussion revolves around the representation of the function f(x) defined as a series involving alternating terms. Participants explore whether this function can be expressed as an elementary or special function, examining its series expansion and potential simplifications.

Discussion Character

  • Exploratory, Technical explanation, Mathematical reasoning

Main Points Raised

  • One participant asks if the function f(x) = ∑_{k=1}^∞ (-1)^n / x^{2k} can be represented as an elementary or special function.
  • Another participant suggests breaking down the function into two separate series for further analysis.
  • A different participant proposes a simplification of the series, arriving at the expression -1/(1 + x^2) and seeks validation for this result.
  • One participant confirms the correctness of the simplification and notes that it represents a geometric series with a specific ratio.
  • A participant expresses self-criticism for not recognizing the simplification earlier.

Areas of Agreement / Disagreement

There appears to be some agreement on the correctness of the simplification provided, but the initial question regarding the representation of f(x) as a special function remains open for further exploration.

Contextual Notes

The discussion does not clarify any assumptions regarding the convergence of the series or the definitions of the terms involved, which may affect the conclusions drawn.

pierce15
Messages
313
Reaction score
2
Hi, does anyone know if this function:

[tex]f(x) = \sum_{k=1}^\infty \frac{(-1)^n}{x^{2k}}[/tex]

is representable as an elementary or already defined special function? Thanks
 
Physics news on Phys.org
This function can be broken up as:

[tex]f(x) = \sum_{k=1}^\infty x^{4k} - \sum_{n=1}^\infty x^{4n-2}[/tex]

Any ideas?
 
I think I've got it: the above expression is equal to

[tex]\frac{1}{x^4 - 1} - \frac{ x^2} {x^4 - 1} = - \frac{1}{1 + x^2}[/tex]

does that look ok?
 
piercebeatz said:
I think I've got it: the above expression is equal to

[tex]\frac{1}{x^4 - 1} - \frac{ x^2} {x^4 - 1} = - \frac{1}{1 + x^2}[/tex]

does that look ok?

Answer is correct. It is a geometric series, ratio = -1/x2.
 
Oh, right. I'm an idiot for not seeing that to begin with
 

Similar threads

  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
4K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K