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[Octave-bug-tracker] [bug #41453] norm is really slow for sparse matrice
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From: |
Carlo de Falco |
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Subject: |
[Octave-bug-tracker] [bug #41453] norm is really slow for sparse matrices |
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Date: |
Tue, 04 Feb 2014 11:36:06 +0000 |
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User-agent: |
Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:26.0) Gecko/20100101 Firefox/26.0 |
Follow-up Comment #1, bug #41453 (project octave):
I don't know how "norm (A, 2)" is currently computed for
a sparse matrix, but probably we should use "svds (A, 1, 'L')"
instead, at least with your test this works better:
for s = [50 100 150]
for i = 1:5
A = sprand (s, s, 0.1);
tic();
n1 = svds (A, 1);
t1 = toc();
tic();
n2 = norm (full (A));
t2 = toc();
printf (["Norm diff: %g, sparse time: %g,", ...
"full matrix time: %g. Speed x: %g\n"],
abs (n1-n2) / n1, t1, t2, t1/t2);
end
end
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