What is the Fourier transform of 1/x?

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Discussion Overview

The discussion revolves around the Fourier transform of the function \( f(x) = \frac{1}{x} \). Participants explore the integrability of this function and its implications for the existence of a Fourier transform, particularly in the context of generalized or distributional Fourier transforms.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that \( \frac{1}{x} \) is not integrable over \( \mathbb{R} \), which complicates the existence of a Fourier transform.
  • Another participant agrees that \( \frac{1}{x} \) is not square integrable, particularly due to its behavior as \( x \) approaches 0.
  • A later reply mentions that \( \frac{1}{x} \) can exist distributionally as \( \frac{\pi}{2}(H(u)-H(-u)) \), suggesting a potential form for the Fourier transform.
  • One participant references the integral of \( \frac{\sin(ax)}{x} \) as a related concept that may help in understanding the Fourier transform of \( \frac{1}{x} \).

Areas of Agreement / Disagreement

Participants generally agree that \( \frac{1}{x} \) is not square integrable and that its behavior near zero poses a problem. However, there is no consensus on the explicit form of the generalized Fourier transform, and multiple views on its distributional existence are presented.

Contextual Notes

The discussion highlights limitations regarding the integrability of \( \frac{1}{x} \) and its behavior near the origin, which are critical to understanding the Fourier transform in this context.

nonequilibrium
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Hello.

I understand that in the form of \int_{\mathbb R} f(x) \exp{2 \pi i tx} \mathrm d x the function f: \mathbb R \to \mathbb C: x \to \frac{1}{x} doesn't have a Fourier transform (because the function is not integrable).

But in my analysis course, there is a theorem that states that in L^2(\mathbb R) there is a unique extension to the Fourier transform for all square-integrable functions (so also the above-defined f). It does, however, not give an explicit form. So I was wondering, what would this generalized Fourier transform of f look like? Is it known explicitly?

Thank you!

EDIT: apologies! I was too fast in typing, of course 1/x is not square-integrable around the origin, so just cut out the [-1,1] interval and replace it with zero. My main question is how the function behaves for large x.
 
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1/x is not square integrable. (Behavior as x -> 0 is problem).
 
the "EDIT" was there well before you posted though
 
mathman said:
1/x is not square integrable. (Behavior as x -> 0 is problem).

it exist distributionally as \frac{\pi}{2}(H(u)-H(-u))

remember the integral of \frac{sin(ax)}{x} and you will get the answer
 

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