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re: Speed concerns with fft

From: Joe Koski
Subject: re: Speed concerns with fft
Date: Fri, 08 Oct 2004 09:41:50 -0600
User-agent: Microsoft-Entourage/

on 10/8/04 7:15 AM, Sébastien Maerten at address@hidden

> Hello,
> I need to perform fft on "large" sets of data, for that I've used
> octave binary installed by fink on macosx 10.3.5 on an ibook G4 1GHz (
> 256 Mo RAM). It turns out that computing fft( my_data ) takes about 15
> sec when my_data is a 500K floats vector (timed by tic() ; fft () ;
> toc() ). With a 1M floats vector, the time jumps to 6000 sec !
> Do anybody know if this is the intended behavior ? ( I don't know a
> word about fft algorythms )

Another potential issue is whether you are running out your 256 Mb of
physical memory and going to virtual memory on the hard disk. That can
really slow things down. Take a look at "top" in another window
while the fft is in progress to see how memory is being used.


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