Talk:Butterfly diagram

Viterbi Trelliss
The article currently states that the Butteryfly structure is also found in the Viterbi Algorithm. As far as I can tell, these really have nothing to do with one another. The Viterbi trellis recognizes that the decoding tree actually merges repeatedly, which we recognize today as dynamic programming. I suggest removing the reference to the Viterbi Algorithm.Intellec7 (talk) 22:42, 21 November 2014 (UTC)

When was it coined
If anyone has a reference to where this term was coined, I'd be curious to know. (From a literature search, it seems to have been common terminology as early as the mid-1970s.) &mdash;Steven G. Johnson 02:41, 21 September 2005 (UTC)
 * here (original ) - it says "1904 Edward Maunder plots the first sunspot "butterfly diagram""
 * I'm not sure what that means.. but maybe its a lead. Fresheneesz 00:20, 24 April 2006 (UTC)
 * That's referring to something completely different, unfortunately: see Solar cycle. I'll add a disambiguation header.  —Steven G. Johnson (talk) 02:07, 26 February 2009 (UTC)

more than 2 inputs
How do buttefly diagrams work with more than two inputs? It seems like inputs have to be switched around.. I think i'll know how to generalize this by the end of the week (I have a project I need to know this for). Fresheneesz 00:20, 24 April 2006 (UTC)


 * They are just a linear network in general (a directed acyclic graph where vertices correspond to additions and edges correspond to multiplications by constants). Of course, in the general case, they don't resemble butterflies. Hmm, it looks like we are missing an article on linear networks. —Steven G. Johnson (talk) 02:08, 26 February 2009 (UTC)

Wnk
I've been running across Wnk in looking at FFT and butterfly diagrams.

I've seen definitions that $$W_n^k = \mathbf{cos}\bigg(\frac{-2 k \pi}{N}\bigg) + i \mathbf{sin}\bigg(\frac{-2 k \pi}{N}\bigg) = \mathbf{e}^{(\frac{-2 k \pi}{N})} $$
 * where i is the imaginary unit.

What does it correspond to? Fresheneesz 01:39, 24 April 2006 (UTC)

More correctly: $$W_N^k = \mathbf{cos}\bigg(\frac{-2 k \pi}{N}\bigg) + i \mathbf{sin}\bigg(\frac{-2 k \pi}{N}\bigg) = \mathbf{e}^{(\frac{-2 k \pi i}{N})} $$. This is the k-th basis vector for an N-point digital Fourier transform, which is the thing calculated by the FFT algorithm. See my tutorial. -- Bartosz 15:49, 28 April 2006 (UTC)


 * $$W_N$$ is merely an Nth primitive root of unity. It is commonly denoted $$\omega_N$$ (I get the impression that "W" is an artifact of older papers where typesetting Greek letters was difficult.) —Steven G. Johnson 20:43, 28 April 2006 (UTC)

XBM images
This external link explanation of butterfly diagrams specifically leads to pages with XBM images that are not displayed by most browsers (I tried IE and Firefox). It's some really bad XWindows ASCII format. I'm wondering about the usefulness of this link. -- Bartosz 03:31, 28 April 2006 (UTC)
 * No problem now on modern Firefox (3.0.8). --Thenickdude (talk) 12:20, 16 April 2009 (UTC)

Has broader application
It seems wikipedia has no page on butterfly networks in general. The structure built by recursively applying a butterfly is not only useful for FFTs, but many general computing problems - especially parallel systems. I'm not sure how to best go about expanding this. --141.218.144.34 (talk) 21:39, 17 November 2009 (UTC) For example the Walsh Hadamard transform or you might even want to perform a permuation using such a thing. It is a very useful and under explored structure to be sure. — Preceding unsigned comment added by 14.162.191.168 (talk) 15:22, 20 February 2014 (UTC)

Inline TeX
If the view from your browser is like that from mine, then on the line above, you see the second omega placed much lower than the surrounding letters. Obviously that's wrong. This is one of several reasons from avoiding TeX in an "inline" setting, even though it works well in a "displayed" setting. Michael Hardy (talk) 03:55, 6 January 2010 (UTC)
 * replacing $$\omega\,$$ with $$\omega^{-1}\,$$ and

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