Talk:Butterfly diagram

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[edit] 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.) —Steven G. Johnson 02:41, 21 September 2005 (UTC)

here (original [1]) - 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)

[edit] 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)

[edit] 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)

WN is merely an Nth primitive root of unity. It is commonly denoted ωN (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)

[edit] 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)

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