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Re: 2D FFT Slow. Any ideas? [message #37367 is a reply to message #37234]

Mon, 08 December 2003 12:17

Richard French
Messages: 173
Registered: December 2000

Senior Member

On 12/8/03 3:02 AM, in article
64b518634e4a83f7473363b5cd15989d@news.teranews.com, "Brian"
<brian.huether@NOdlrSPAM.de> wrote:

> Hi,
>
> The IDL code is
>
> A=dcomplex(randomn(seed,2048, 2048,/DOUBLE), randomn(seed,2048,
> 2048,/DOUBLE))
> t=systime(1)
> FA=fft(A,-1)
> print, systime(1)-t
>
> The corresponding matlab code is
>
> A = randn(2048,2048) + i*randn(2048,2048);
> tic; FA=fft2(A); toc
>
> I get around 10.4 sec in IDL, and around 3.7 sec in MATLAB 6.5
>
> -brian
>

I got FFTW working on a SUNBLADE 1000
IDL> print,!VERSION
{ sparc sunos unix Solaris 6.0 Jun 27 2003 32 64}

(I had to run IDL in 32-bit mode)

For a REAL FFT, 1024x1024, IDL took 2.9 times as long as FFTW
For 2048 x 2048, IDL took 3.4 times as long as FFTW.

On a Dec/HP/Compaq Alpha, the speedup was a factor of 4 for 1024x1024 and
about a factor of 5 for 2048x2048.

If you have lots of FFT's to compute, it is worth taking the trouble to
build a DLM for the FFTW routines. However, I did not find this easy to do,
I used the help from Stein Haugan, and I had to fiddle with the Makefile to
get everything working.

I am going to see if I can get fftw to work under MAC OS X, and to build a
DLM for that. If anyone has already succeeded in doing this, I'd be
interested in knowing how you did it.

Dick French

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[Message index]

		Re: 2D FFT Slow. Any ideas? By: Brian on Mon, 08 December 2003 00:02
		Re: 2D FFT Slow. Any ideas? By: R.G. Stockwell on Fri, 05 December 2003 13:05
		Re: 2D FFT Slow. Any ideas? By: K. Bowman on Fri, 05 December 2003 10:32
		Re: 2D FFT Slow. Any ideas? By: R.G. Stockwell on Fri, 05 December 2003 10:04
		Re: 2D FFT Slow. Any ideas? By: Richard French on Mon, 08 December 2003 12:17

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