[SciPy-user] FFT speed ?

Samuel GARCIA sgarcia@olfac.univ-lyon1...
Wed Feb 7 08:07:48 CST 2007


Yes it is pretty fast.
The difference of time is not a problem for the end user (between 0.2
and 1 s).
But specialy the value of 186889 is really a problem, the computation is
infinit.
Did you try tis value especialy ?




Christian Kristukat wrote:
> Samuel GARCIA wrote:
>   
>> Hello list,
>>
>> I have a problem with fft speed.
>> could someone try this :
>>
>> from scipy import *
>> import time
>>
>> a = rand((186888));t1=time.time();fft(a);t2=time.time();t2-t1
>>
>> # for me about 0.67791390419006348 s. on centrino 1.6GHz
>>
>> a = rand((186890));t1=time.time();fft(a);t2=time.time();t2-t1
>>
>> # for me about 1.622053861618042 s. on centrino 1.6GHz
>>
>> a = rand((186889));t1=time.time();fft(a);t2=time.time();t2-t1
>>
>> # the computation is infinit !!!! (no time to wait)
>>
>>
>> Question : why is there a problem specialy for that size (186889) of fft ?
>> It is not the only size with that problem.
>>     
>
> I guess this is due to the design of fft which is made for input lengths of
> 2**x. If you try e.g. 262144=2**18 which is even larger than 186889 you'll see
> that it's pretty fast.
>
> Christian
>
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>   

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Samuel Garcia
Universite Claude Bernard LYON 1
CNRS - UMR5020, Laboratoire des Neurosciences et Systemes Sensoriels
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FRANCE
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