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Re: FFT in 1 dimension [message #28494 is a reply to message #28492]

Fri, 07 December 2001 13:41

Wayne Landsman
Messages: 117
Registered: January 1997

Senior Member

hradilv.nospam@yahoo.com wrote:

> Here's what I came up with. Any comments?

I haven't examined your code in detail, but there is one line where the
speed of the program can be improved significantly:

Instead of writing

for i=0, nlines-1 do fdata[*,i] = fft(fdata[*,i],inverse=inverse)

write

for i=0, nlines-1 do fdata[0,i] = fft(fdata[*,i],inverse=inverse)

I'm actually not sure why this speed things up. I suppose by writing
fdata[0,i] on the left hand side, you've directly specified a starting
location to place the computation, but if you instead write fdata[*,i]
then IDL first extracts a temporary variable, assigns it to the value of
the computation, and then writes the temporary variable back into
fdata. Still, I would think that the compiler could recognize that
these two notations are equivalent.

--Wayne Landsman landsman@mpb.gsfc.nasa.gov

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[Message index]

		Re: FFT in 1 dimension By: Paul Woodford on Fri, 07 December 2001 20:09
		Re: FFT in 1 dimension By: Wayne Landsman on Fri, 07 December 2001 13:41
		Re: FFT in 1 dimension By: hradilv.nospam on Fri, 07 December 2001 12:10
		Re: FFT in 1 dimension By: hradilv.nospam on Fri, 07 December 2001 11:05

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