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Re: 'for' loop vectorization


From: Hermann Schwarting
Subject: Re: 'for' loop vectorization
Date: Tue, 23 Oct 2007 21:43:00 +0200
User-agent: KMail/1.9.7

Am Dienstag, 23. Oktober 2007 schrieb Alexander Barth:

> What about this:
> i = 2:r;
> j = 2:c;
> D(i, 1) = max(D(i-1, 1), D(i, 1));
> D(1, j) = max(D(1, j-1), D(1, j));
> D(i,j) = max(D(i,j), min( D(i,j-1), min(D(i-1,j-1), D(i-1,j)) ));
>
> I have tested it for a random matrix.
> Does this work for you?

No, sorry. Probably I should have stated the problem with more detail. 
The inner for-loop operates in place and the value of one element is 
dependent on the previous value left of it and those of the row above 
it. So the results are not identical. It may happen by chance that 
the value of D(r,c) is the same.

The more I think about it, it looks like I can’t vectorize this. It’s 
a bit similar to a cumulative maximum, which can’t be vectorized 
either, I think.

I’ll take the route of putting it in an oct file and see if that works 
out.

Alexander, thank you for your time in any case!

Kind regards,
Hermann


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