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[Octave-bug-tracker] [bug #41453] norm is really slow for sparse matrice


From: Massimiliano Fasi
Subject: [Octave-bug-tracker] [bug #41453] norm is really slow for sparse matrices
Date: Tue, 01 Apr 2014 12:20:47 +0000
User-agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:28.0) Gecko/20100101 Firefox/28.0

Follow-up Comment #12, bug #41453 (project octave):

I hadn't got over 1000 x 1000, but to answer your question I have run some
experiments, whose results are


>> A = sprandn(10, 10, 0.1); tic, norm(A); toc
Elapsed time is 0.000300884 seconds.
>> A = sprandn(100, 100, 0.1); tic, norm(A); toc
Elapsed time is 0.00775719 seconds.
>> A = sprandn(1000, 1000, 0.1); tic, norm(A); toc
Elapsed time is 4.24463 seconds.
>> A = sprandn(2000, 2000, 0.1); tic, norm(A); toc
Elapsed time is 33.6406 seconds.
>> A = sprandn(4000, 4000, 0.1); tic, norm(A); toc
Elapsed time is 220.658 seconds.
>> A = sprandn(8000, 8000, 0.1); tic, norm(A); toc
Elapsed time is 1587.18 seconds.


for the patched version of the norm and


>> A = sprandn(10, 10, 0.1); tic, norm(A), toc
Elapsed time is 0.0279908 seconds.
>> A = sprandn(100, 100, 0.1); tic, norm(A), toc
Elapsed time is 3.31705 seconds.
>> A = sprandn(1000, 1000, 0.1); tic, norm(A), toc
Elapsed time is 333.631 seconds.
>> A = sprandn(2000, 2000, 0.1); tic, norm(A); toc
Elapsed time is 1433.76 seconds.


for the old version. I haven't tried larger matrices with the old norm as it
would have lasted hours.

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