Even function has a Laurent decomposition of even functions and even powers of z

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Discussion Overview

The discussion revolves around the properties of even functions and their Laurent decompositions, specifically whether the components of the decomposition can also be expressed as even functions with even powers of z. The scope includes mathematical reasoning and exploration of function properties.

Discussion Character

  • Exploratory, Mathematical reasoning

Main Points Raised

  • One participant questions how to determine if the Laurent decomposition of an even function results in even functions and even powers of z.
  • Another participant suggests computing the even and odd parts of a generic Laurent series to explore the properties of even functions.
  • A participant notes the definition of an even function, stating that for an even function f(z), it holds that f(z) = f(-z), leading to a relationship involving the coefficients a_n of the series.
  • The same participant expresses uncertainty about how to proceed from their findings to prove that the components f0(z) and f1(z) are even functions with only even powers of z.
  • One participant emphasizes that the series must be in powers of z.

Areas of Agreement / Disagreement

Participants do not reach a consensus; there are multiple viewpoints and ongoing questions regarding the properties of the Laurent decomposition of even functions.

Contextual Notes

There are limitations regarding the assumptions made about the coefficients and the nature of the Laurent series, as well as the definitions of even and odd functions that may affect the conclusions drawn.

caramello
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Hi,

if let's say that there's an even function f(z) then how do we know if its Laurent decomposition (i.e. f(z) = f0(z) + f1(z) ) will be even functions and have even powers of z?

Any help will be greatly appreciated.
 
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Take a generic Laurent series and compute it's even and odd parts. What do you see?

(You know a formula for the even and odd part of any function, right?)
 
i know that for even function f(z) = f(-z) which means that the sum from n=0 to infinity of a_n z^n is equals to the sum from n=0 to infinity of a_n (-z)^n.
(note: a_n is the coefficient of the series)

Then this will give me an equation of a_n = a_n (-1)^n ---> conclusion: a_n can't be equal to 0, am I right?

But then after this I don't know what else to do in order to prove that f0(z) and f1(z) are even functions that only has powers of z.

Thank you so much
 
Must be Laurent series in powers of z.
 

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