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Re: Optimizing loops [message #92398 is a reply to message #92368]

Tue, 08 December 2015 08:28

Phillip Bitzer
Messages: 223
Registered: June 2006

Senior Member

On Wednesday, December 2, 2015 at 1:04:33 PM UTC-6, sam.t...@gmail.com wrote:
> If anyone has optimization suggestions, please let me know! Thanks :)

In addition to the suggestions that Sergey provided, let's add a couple more:

> ind14 = WHERE(dist LE 14.)
> land14 = land_mask(ind14)
> landy = WHERE(land14 EQ 0, landy_cnt)
> land_perc[j] = FLOAT(landy_cnt)/FLOAT(N_ELEMENTS(land14))*100

For the last line, no need to "float" both numbers. Also, you might consider either a) dropping the *100 and do that at the end or b) reordering the operations so that you don't need to call FLOAT at all. Consider:

IDL> 1/2 ;we know this is not the number we are looking for
IDL> 1/FLOAT(2) ;closer, but we'll have to multiply the final array by 100
IDL> 100.0 * 1/2 ;this works, but only if the "100.0" comes first

Also, you don't need to count the number of elements in land14 - you already have that information. It's the same size as ind14, and you can get that size using the count argument.

Further, x*x is faster than x^2...although the cost/benefit depends on the size of the arrays.

Finally, there *is* a way to further vectorize your code. But, whether it's worth it depends on the size of the land/sat arrays. There's some black magic using rebins, pound signs, etc.

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[Message index]

		Optimizing loops By: sam.tushaus on Wed, 02 December 2015 11:04
		Re: Optimizing loops By: Sergey Anfinogentov on Thu, 03 December 2015 02:10
		Re: Optimizing loops By: Phillip Bitzer on Tue, 08 December 2015 08:28
		Re: Optimizing loops By: MarioIncandenza on Tue, 08 December 2015 11:05
		Re: Optimizing loops By: Russell[1] on Wed, 09 December 2015 08:29

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