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Re: [Help-gsl] Requesting feedback on the FFT interface

From: Dimitris Papavasiliou
Subject: Re: [Help-gsl] Requesting feedback on the FFT interface
Date: Mon, 15 May 2006 23:52:37 +0300
User-agent: Mail/News 1.5 (X11/20060228)

Brian Gough wrote:
Dimitris Papavasiliou writes:
> 3) Well I suppose there's a good reason for this but the halfcomplex > arrays produced by radix2 and mixed-radix routines are different.
The Radix-2 ffts are designed to operate inplace without using any
extra memory, so the layout is a consequence of that constraint and
the algorithm.
If memory is not an issue it is fine to use the Mixed Radix routines
for size N=2^k to get the same layout.  There is no requirement to use
radix 2 routines in that case
Well as it turns out that permutation is a major bottleneck anyway. Well I should be ashamed to think I could get away with O(N^2) complexity because they were "just swaps" (although the swaps were made using gsl_vector_swap_elements which probably means two multiplications and additions per swap; it could be optimized more). That was a minor point anyway.

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