Speed concerns with fft

[Sébastien Maerten]

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 )

I'm sorry I can't provide more info about octave's build options than 
it's current fink version.

Do anybody know how I can get a "faster" result ? Building octave with 
proper math libraries ? Which one ? It seems to me that building octave 
from source on osx is not trivial (I've failed with fink, darwinports 
and manually with versions 2.1.57 , 2.1.59 and 2.1.60), btw, is it 
worth reporting such build failures ?

I'm in trouble because I *need* those fft's but I can't give the 
computer around 100 x 6000 sec just for tha :( .

Any idea / pointer / help would be greatly apreciated. Thanks.



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