Expressing Function Norm Using Fourier Coefficients

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Discussion Overview

The discussion revolves around expressing the norm of a function using Fourier coefficients, specifically exploring the L² norm and its relationship with Fourier series. Participants inquire about the process and implications of this expression for a given function.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions which norm is being referred to, suggesting that the L² norm can be expressed as the square root of the sum of the squares of the Fourier coefficients.
  • Another participant provides a specific example involving the function f(x)=ae^(-ix)+b+ce^(ix) and asks how to express its norm in terms of Fourier coefficients, noting the ambiguity regarding the type of norm.
  • A different participant asserts that it is only the L² norm that applies, stating that the L² norm of the time-domain function equals the L² norm of the frequency-domain data, and suggests that the L² norm of the given function is a² + b² + c².

Areas of Agreement / Disagreement

There is no consensus on which norm is being discussed, as participants have differing views on the applicability of the L² norm and its expression in terms of Fourier coefficients.

Contextual Notes

The discussion lacks clarity on the specific type of norm being referenced, and assumptions regarding the function and its properties are not fully articulated.

sristi89
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Hi,

I was wondering if it is possible to express the norm of a function in terms of Fourier coefficient. If so, how do you go through it if given a particular function.

Thanks
 
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What norm? The L^2-norm can be expressed, and it is the square root of the sum of the squares of the coefficients.
 
Here is a sample question:

What are the Fourier coefficients of the function f(x)=ae^(-ix)+b+ce^(ix)? And express the norm in terms of Fourier coefficients.

They don't mention if it is the L^2 norm or not.
 
well, it's only the L2 norm (a measure of energy) in which the L2 norm of the time-domain function (over one period) is equal to the L2 of the frequency-domain data (the Fourier coefficients).

i think the L2 norm of your f(x) is a2 + b2 + c2.
 

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