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Hi! Sorry to ask what is probably a really clueless question -- if there are any obvious sources of information about this, I'd be happy to go there and find this out for myself... :] Anyway; I'm trying to produce a graph to illustrate a time sequence indexing method, which relies on extracting the low-frequent Fourier coefficients and indexing a vector consisting of those. The graph should contain the original time sequence, and one reconstructed from the Fourier coefficients. Since it is reconstructed from only the low-frequent coefficients (perhaps 10-20 coefficients), it will look wavy and sinus'y. Now... I'm no expert in signal processing (or the specifics of FFT/DFT etc.), and I can't seem to make the FFT module do exactly what I want here... It seems that using fft(seq).real extracts the coefficients I'm after (though I'm not sure whether the imaginary components ought to figure in the equation somehow...) But no matter how I use inverse_fft or inverse_real_fft it seems I have to supply a number of coefficients equal to the sequence I want to approximate -- otherwise there will be a huge offset between them. Why is this so? Shouldn't the first coefficient take care of such an offset? Perhaps inverse_fft isn't doing what I think it is? If I haven't expressed myself clearly, I'd be happy to elaborate... (For those who might be interested, the approach is described in the paper found at http://citeseer.nj.nec.com/307308.html with a figure of the type I'm trying to produce at page 5.) Anyway, thanks for any help :) -- Magnus Lie Hetland The Anygui Project http://hetland.org http://anygui.org
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Magnus Lie Hetland