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From: &quot;uC&quot; &lt;bla.bla@uc.uc&gt;
Newsgroups: comp.soft-sys.matlab
Subject: FOR loops performance - 32bit vs 64 bit Matlab
Date: Sat, 2 Aug 2008 10:58:54 +0200
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Hi all,

Yesterday I have written tha post entitled &quot;density matrix conversion - 
vectorization&quot; where I needed some help regarding vectorization to improve 
the speed. It turned out that in fact I don't need to vectorize it and 
performance problem is somewhere else.

There are three loops:

for n=1:col_no
        for m=1:row_no
            for k=1:D(m, n)
                [SOME SIMPLE ARITHMETIC OPERATIONS]
            end
            if rand() &lt; D(m, n)-floor(D(m, n))
               [SOME SIMPLE ARITHMETIC OPERATIONS]
            end
        end
    end
end

On 32 bit system (XP Pro) and Matlab (2006a) it takes ~17 seconds to finish 
these operations but on 64 bit (Win 2003 Serv. End. Ed.) and 64 bit Matlab 
(2007b) it takes 370 secons!!!

Now the most interesting... when I substitute exact numbers for &quot;col_no&quot; and 
&quot;row_no&quot; (6700 and 7100 in tested case) 64 bit Matlab needs only 8 seconds 
to finish, when on 32 bit one timings remains almost untouched!

32 bit machine is dual core Athlon64x2 2GHz with 2 GB RAM
64 bit machine is dual socket dual core Opteron 2218 2.6 GHz with 8 GB RAM

Does anyone have an idea if it is a Matlab bug or anything else?

Best wishes,
uC 


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