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Re: FOR loops removal [message #62057 is a reply to message #61972]

Wed, 20 August 2008 00:24

loebasboy
Messages: 26
Registered: August 2008

Junior Member

On Aug 19, 3:43 pm, Wox <nom...@hotmail.com> wrote:
> On Tue, 19 Aug 2008 05:38:50 -0700 (PDT), loebasboy
>
> <stijn....@gmail.com> wrote:
>> FOR l = 0, n*2 DO BEGIN
>> temp = 0
>> FOR i =0,max_y-1 DO BEGIN
>> FOR j=0,max_x-1 DO BEGIN
>> jtemp = j + l
>> jtemp2 = j + n
>> temp = temp + (arr[i,jtemp] * arr [i,jtemp2])
>> ENDFOR
>> ENDFOR
>> output[l] = temp/(max_x*max_y)
>> ENDFOR
>
> The code below is a start. Does this processing have a name? It feels
> familiar somehow. Btw, in IDL the first index of an array is the
> column and the second is the row. So in your case y are the columns
> and x are the rows. No problem with that off course, just check
> whether this is how you intended it.
>
> n = 8
> max_x = 5
> max_y = 5
> output = fltarr(2*n+1)
> arr = findgen(max_y, 2*n+max_x) +1
>
> arr2=arr[0:max_y-1,n:max_x-1+n]
> FOR l = 0, 2*n DO $
> output[l] = total(arr[0:max_y-1,l:max_x-1+l]*arr2)
> output/=max_x*max_y

Thank you for your code, it works rather well, maybe it seems familiar
because it's a kind of autocorrelation that I'm calculating... .

I think I still need some vectorisation training to get IDL much
faster, I've calculated a time profit of 14 h (that makes 8.5 h
instead of 22.5 h), so I still have some FOR loops I can train on ;).
Thanks for helping finding my way and the fast answers, I think I will
definitely post again when I'm really stuck again ;).

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[Message index]

		Re: FOR loops removal By: David Fanning on Tue, 19 August 2008 06:51
		Re: FOR loops removal By: Wox on Tue, 19 August 2008 06:43
		Re: FOR loops removal By: Jeremy Bailin on Wed, 20 August 2008 04:50
		Re: FOR loops removal By: loebasboy on Wed, 20 August 2008 00:24
		Re: FOR loops removal By: Chris[6] on Tue, 19 August 2008 13:04

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