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Re: Bug in IDL {alpha OSF unix 4.0.1} SMOOTH() [message #7469 is a reply to message #7468]

Tue, 19 November 1996 00:00

steinhh
Messages: 260
Registered: June 1994

Senior Member

> For some reason, the smoothing introduces non-zero values in the result array along
> one column, and I cannot understand why..

Here I go, following up my post after only a few minutes... I just realized that SMOOTH
is probably using some kind of FFT convolution to perform the smoothing operation,
even though the /edge_truncate was set. With fourier transforms back and forth, (numerical)
errors of this magnitude are not uncommon, one should even *expect* them (and therefore
treat the results with care, like checking "smooth(...) gt 1e-3" rather than "... gt 0").

So, it's a *feature*, not a bug, I guess :-)

Funny thing, what tipped me off was that when I rewrote my program to use CONVOL instead
of SMOOTH, the speed went way down.

Stein Vidar H. Haugan

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		Bug in IDL {alpha OSF unix 4.0.1} SMOOTH() By: steinhh on Tue, 19 November 1996 00:00
		Re: Bug in IDL {alpha OSF unix 4.0.1} SMOOTH() By: steinhh on Tue, 19 November 1996 00:00

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