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Re: simple vectorizing problem [message #62457 is a reply to message #62427]

Tue, 09 September 2008 02:58

Foldy Lajos
Messages: 268
Registered: October 2001

Senior Member

On Tue, 9 Sep 2008, Chris wrote:

> Looks like the memory allocation overhead associated with
> vectorization is worse than looping:
>
> vectorization 1 time: 5.0360808 s
> vectorization 2 time: 4.8453941 s
> looping itme: 4.0875931 s
>
> The vectorization performances become comparitvely worse as the array
> grows (both reform() and total() create temporary, large arrays).
>
> chris
>
> pro test
>
> nimage = 1500
> im = fltarr(512,512,nimage)
>
> t0 = systime(/seconds)
> mean=total(reform(im,512L*512L, nimage), 1)/(512.*512)
> t1=systime(/seconds)
>
> mean=total(total(im,1),1)/(512.*512.)
>
> t2 = systime(/seconds)
>
> for i=0, nimage-1, 1 do $
> mean[i]=total(im[*,*,i])/(512.*512)
>
> t3=systime(/seconds)
>
> print, t1-t0
> print, t2-t1
> print, t3-t2
>
> end
>
>

try this:

t0 = systime(/seconds)
mean=total(reform(im,512L*512L, nimage, /overwrite), 1)/(512.*512)
; ^^^^^^^^^^^^
t1=systime(/seconds)

regards,
lajos

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[Message index]

		Re: simple vectorizing problem By: David Fanning on Wed, 10 September 2008 17:14
		Re: simple vectorizing problem By: dpm314 on Wed, 10 September 2008 16:53
		Re: simple vectorizing problem By: Foldy Lajos on Tue, 09 September 2008 02:58
		Re: simple vectorizing problem By: Chris[6] on Tue, 09 September 2008 01:50
		Re: simple vectorizing problem By: David Fanning on Mon, 08 September 2008 19:17
		Re: simple vectorizing problem By: dpm314 on Mon, 08 September 2008 18:48
		Re: simple vectorizing problem By: JD Smith on Thu, 11 September 2008 11:56
		Re: simple vectorizing problem By: Spon on Thu, 11 September 2008 05:15

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