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Re: octave vs. matlab vectorization

From: matt
Subject: Re: octave vs. matlab vectorization
Date: Tue, 15 Sep 2009 13:01:05 +0100

thanks for the insight on compiler issues.

the matlab JIT compiler is doing something clever in the simple- minded codes i was experimenting with but i realise now that a lot of the problem is the overhead in allocating and defining arrays.

i had a vector q of length 10. in the loops code, it was fast to check through it elementwise; in the (semi) vectorized code, time was being spent setting up q and also tmp and (tmp>50), both length 10.

replacing 10 by 1000 puts the two codes on a par as now the overhead to set up the vectors is relatively small.

in octave, of course, the vectorized version wins by miles.
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