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[Octave-bug-tracker] [bug #46830] Multiplication about 4x slower than Ma

From: Philip Nienhuis
Subject: [Octave-bug-tracker] [bug #46830] Multiplication about 4x slower than Matlab
Date: Tue, 12 Jan 2016 22:35:44 +0000
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:41.0) Gecko/20100101 Firefox/41.0 SeaMonkey/2.38

Follow-up Comment #5, bug #46830 (project octave):

FWIW, with Matlab r2016a prerelease I see that it uses all four CPU cores (of
my i5 PC with 8 GB RAM) when doing

a = rand (1.5e4);
tic; a * a; toc
Elapsed time is 34.337681 seconds.

but at most two cores (~50 % CPU usage) with

a = rand (1.5e4);
a .* a;
Elapsed time is 0.539022 seconds.

(Octave-4.1.0+ needs ~42 sec and 0.7 sec, resp. and Matlab makes the system
fans clearly emit more noise with a * a.  AFAIK Matlab also invokes the GPU.)

All in all I'd conclude that Octave doesn't behave much differently from
Matlab as regards CPU usage, but might be a little slower as it doesn't use
the GPU.


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