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Re: For loops vs. matrix operations [message #37434 is a reply to message #37433]

Wed, 17 December 2003 18:59

Kenneth P. Bowman
Messages: 585
Registered: May 2000

Senior Member

In article <Z%3Eb.41137$jo.28094@newssvr29.news.prodigy.com>,
"Jonathan Greenberg" <greenberg@ucdavis.edu> wrote:

> array=intarr(10000)
> for i=0,(10000-1) do begin
> array[i]=array[i]+1
> endfor
>
> MUCH slower than:
>
> array=intarr(10000)
> array=array+1

Try timing it and see :-)

n = 1000000
array = LONARR(n)

time0 = SYSTIME(/SECONDS)
FOR i = 0, n-1 DO array[i] = array[i] + 1
time0 = SYSTIME(/SECONDS) - time0

time1 = SYSTIME(/SECONDS)
array = array + 1
time1 = SYSTIME(/SECONDS) - time1

PRINT, 'Speed-up : ', time0/time1

IDL> @time1
Speed-up : 42.071883

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[Message index]

		Re: For loops vs. matrix operations By: David Fanning on Thu, 18 December 2003 04:55
		Re: For loops vs. matrix operations By: marc schellens[1] on Wed, 17 December 2003 23:25
		Re: For loops vs. matrix operations By: Kenneth P. Bowman on Wed, 17 December 2003 18:59
		Re: For loops vs. matrix operations By: JD Smith on Wed, 17 December 2003 17:31
		Re: For loops vs. matrix operations By: James Kuyper on Wed, 17 December 2003 15:52
		Re: For loops vs. matrix operations By: Wonko[3] on Wed, 17 December 2003 15:24
		Re: For loops vs. matrix operations By: Craig Markwardt on Wed, 17 December 2003 14:57
		Re: For loops vs. matrix operations By: mperrin+news on Wed, 17 December 2003 15:05

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