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What Is the Fourier Transform?

quantamagazine.org

11–20 of 214 posts

Re: What Is the Fourier Transform?

#11
post #2

Always blew my mind that every signal can be recreated simply by adding different sine waves together.

Back in my uni days I did not get why that works. Why are sine waves special? Turns out... they are not! You can do the same thing using a different set of functions, like Legendre polynomials, or wavelets.

Another place where functions are approximated is in machine learning which use a variety of non-linear functions for activations, for example the ReLU f(x)= max(0,x)

Re: What Is the Fourier Transform?

#12
post #6

Earlier quoted context omitted.

This kind of statement is too vague to be useful. I even know all the words in there and I still don't know what you mean.

Ask away.

Your earlier post comes off as link-spam, as it uses general language to connect something tangentially related to what you're interested in to drive traffic to your website. This is not conducive to questions.

Re: What Is the Fourier Transform?

#13
post #5
post #2

Always blew my mind that every signal can be recreated simply by adding different sine waves together.

Only if it is band-limited.

No, even functions with non-finite frequency representation. You just need a non-finite number of sines. Nyquist speaks only to a finite number of samples.

Re: What Is the Fourier Transform?

#14
post #12

Earlier quoted context omitted.

Ask away.

Your earlier post comes off as link-spam, as it uses general language to connect something tangentially related to what you're interested in to drive traffic to your website. This is not conducive to questions.

You can still ask.

Re: What Is the Fourier Transform?

#15
post #10

[flagged]

Hmm I always viewed it as sum over orthogonal bases. Sine/Cosine is choice, while there can be many other bases, like Legendre polynomials. Can you explain more how FT is linked to 'a sum over equivalence classes'?

A high level explanation is that a trace counts how many times each equivalence classes appears. In sense, it is similar to a multiset, it associates a count with some input.

In the case of the Fourier transform, it maps from time domain to frequency domain. In the frequency domain, we can see the amplitude (count) of the signal at each frequency.

Re: What Is the Fourier Transform?

#18
post #16

3Blue1Brown made a video with great visualizations: https://www.youtube.com/watch?v=spUNpyF58BY

I’ve dabbled in explaining the FT some, and I think there’s an important trait of that video that needs to be highlighted: it’s a superb demonstration of what the Fourier transform does, mechanically, but it does not at all try to explain why it works in the places we usually apply it or how (having, admittedly, a thoroughly anachronistic mathematical background) you could have invented it.

To be extra clear: it’s a very good video and you should watch it if you don’t have a feel for the Fourier transform. I’m just trying to proactively instil a tiny bit of dissatisfaction with what you will know at the end of it, so that you will then go looking for more.

Re: What Is the Fourier Transform?

#19
post #12

Earlier quoted context omitted.

Your earlier post comes off as link-spam, as it uses general language to connect something tangentially related to what you're interested in to drive traffic to your website. This is not conducive to questions.

You can still ask.

I know and use wavelet, Fourier, and other transforms on a daily basis, but your post did not stimulate any interest in me. Also, your reply on the other thread does not strike me as particularly insightful (I'd argue that your 'frequency decomposition' interpretation is flat-out wrong).

Re: What Is the Fourier Transform?

#20
post #19

Earlier quoted context omitted.

You can still ask.

I know and use wavelet, Fourier, and other transforms on a daily basis, but your post did not stimulate any interest in me. Also, your reply on the other thread does not strike me as particularly insightful (I'd argue that your 'frequency decomposition' interpretation is flat-out wrong).

Are you familiar with the partition function?
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