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Re: Floating Underflow/Overflow [message #27356 is a reply to message #27319]

Thu, 18 October 2001 01:05

bente
Messages: 13
Registered: October 2001

Junior Member

Hi, again.

Wow didnï¿½t expected to get so much response ;-)

> On the other hand, the performance of IDL falls down rather badly when
> dealing with conditional tests on large arrays, especially when FOR
> loops cannot be avoided. Even using WHERE() usually makes a pretty
> large performance hit.

The peformance is the large problem I have, my PC isnï¿½t so fast
(350MHz with only 128MB Ram. And i have to work through a 256x256x128
floating Point array with 3 FOR-Loops (i need the complete Indizes to
get the Radius from a specific point to the current Voxel (donï¿½t no
some faster way to get this)

Itï¿½s not so that this lasts hours then, but i gets annoying if you
want to change a value a bit and then wait several minutes for the
result

> One little trick for avoiding underflows in exponentials might go like
> this. If you wish to compute Y = EXP(-X), for large X, then you can
> usually use a "mask" variable to avoid the underflow.
>
> MASK = (X LT UPPER_LIMIT)
> Y = MASK * EXP(-X*MASK)

Iï¿½ll try this out, thanks for the hint.

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[Message index]

		Re: Floating Underflow/Overflow By: George N. White III on Tue, 16 October 2001 08:19
		Re: Floating Underflow/Overflow By: bente on Tue, 16 October 2001 02:24
		Re: Floating Underflow/Overflow By: Paul van Delst on Mon, 15 October 2001 08:55
		Re: Floating Underflow/Overflow By: Craig Markwardt on Mon, 15 October 2001 07:54
		Re: Floating Underflow/Overflow By: Craig Markwardt on Tue, 16 October 2001 12:18
		Re: Floating Underflow/Overflow By: bente on Thu, 18 October 2001 01:05

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