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[Octave-bug-tracker] [bug #39314] convn(x, y, "valid") produces results


From: Carnë Draug
Subject: [Octave-bug-tracker] [bug #39314] convn(x, y, "valid") produces results that are different from Matlab
Date: Mon, 21 Oct 2013 13:22:24 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130917 Firefox/17.0 Iceweasel/17.0.9

Follow-up Comment #12, bug #39314 (project octave):

I think the cause of the different values comes from the order the values are
added. Looking at the code for inner convolution and comparing to other, it
seems that it's being done in reverse order so machine precision errors get
in. Kind of like in the following example:


octave> a = rand (1, 27);
octave> b = rand (1, 27);
octave> c1 = sum (a .* b);
octave> c2 = sum (a(end:-1:1) .* b(end:-1:1));
octave> c1 - c2
ans =  1.7764e-15
-verbatim

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