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Re: Different FFT times for same array size ? [message #45269]

Wed, 24 August 2005 12:14

Steve Eddins
Messages: 9
Registered: July 2001

Junior Member

"R.G. Stockwell" <no@email.please> wrote:
> "Jan Cami" <jcami@mail.arc.nasa.gov> wrote:
>> A good look at the different input chunks revealed the problem :
>> there's a few NaN values in there which apparently slow it down
>> dramatically. Problem solved !
>
> interesting! I wasn't aware of that time hit with nans.

Yes. NaNs tend to slow down floating-point computations substantially. This
effect isn't specific to IDL. And with FFTs, every output depends
mathematically on every input, so even a single NaN in the input results in
every output value being NaN. This is pretty slow way to create an all-NaN
thing, so the original poster might consider treating inputs with NaNs as a
special case and handling them differently.

Steve

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[Message index]

		Re: Different FFT times for same array size ? By: Steve Eddins on Wed, 24 August 2005 12:14
		Re: Different FFT times for same array size ? By: R.G. Stockwell on Wed, 24 August 2005 11:49
		Re: Different FFT times for same array size ? By: jcami on Wed, 24 August 2005 11:15
		Re: Different FFT times for same array size ? By: jcami on Wed, 24 August 2005 11:01
		Re: Different FFT times for same array size ? By: R.G. Stockwell on Wed, 24 August 2005 09:54

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