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Re: Vectorizing Code [message #29657 is a reply to message #29527]

Thu, 28 February 2002 08:35

James Tappin
Messages: 54
Registered: December 1995

Member

Marc Schellens wrote:

>>> sa = 10.^2*EXP(-ABS(REBIN(LINDGEN(nstate), nstate, nvec, /SAMPLE) - $
>>> REBIN(REFORM(LINDGEN(nvec), 1, nvec), nstate, nvec, /SAMPLE))*dz/h)
>>
>> I am afraid I'd rather stick with the optimized loops than something that
>> takes me five minutes to figure out :-(
>> Pavel
>
> but unfortunately in IDL it may save you more than five
> minutes at run-time if you do figure it out...
> :-) marc
>

Loops aren't as bad as they used to be. Many years ago (IDL 2.x on VMS) I
wrote a very clever (IMHO) routine for time-averaging irregularly sampled
data which speeded things up about 10-fold. However recently (now with IDL
5.x on Linux and Solaris) it became clear that this same time averaging
routine was a major bottleneck. Replacing it with a version with one more
loop and many less temporary arrays speeded up 100-fold in some cases.

The moral: Nowadays loops may be slow but creating and destroying workspace
arrays is often even slower.

James

--
+------------------------+-------------------------------+-- -------+
| James Tappin | School of Physics & Astronomy | O__ |
| sjt@star.sr.bham.ac.uk | University of Birmingham | -- \/` |
| Ph: 0121-414-6462. Fax: 0121-414-3722 | |
+--------------------------------------------------------+-- -------+

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[Message index]

		Re: Vectorizing Code By: marc schellens[1] on Wed, 27 February 2002 22:17
		Re: Vectorizing Code By: Pavel Romashkin on Wed, 27 February 2002 21:43
		Re: Vectorizing Code By: Kenneth P. Bowman on Wed, 27 February 2002 18:56
		Re: Vectorizing Code By: Jeff Guerber on Wed, 27 February 2002 16:00
		Re: Vectorizing Code By: K. Bowman on Thu, 28 February 2002 07:43
		Re: Vectorizing Code By: James Tappin on Thu, 28 February 2002 08:35

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