Fri 29 May 2015 07:58:07 PM UTC, comment #2:
OK well it appears I am the king of erroneous bug reports this week. Sorry about that :(
This is what I ran:
getenv('OPENBLAS_NUM_THREADS')
A=randn(4000);
tic;AA=A'*A;toc
tic;chol(AA);toc
tic;svd(A);toc
and these are the timings:
Compiled with NO_LAPACK=1 (current default in MXE)
-------------------------
>> getenv('OPENBLAS_NUM_THREADS')
ans = 1
>> A=randn(4000);
>> tic;AA=A'*A;toc
Elapsed time is 11.7313 seconds.
>> tic;chol(AA);toc
Elapsed time is 4.23956 seconds.
>> tic;svd(A);toc
Elapsed time is 60.8286 seconds.
>> getenv('OPENBLAS_NUM_THREADS')
ans = 2
>> A=randn(4000);
>> tic;AA=A'*A;toc
Elapsed time is 6.40621 seconds.
>> tic;chol(AA);toc
Elapsed time is 2.50854 seconds.
>> tic;svd(A);toc
Elapsed time is 47.2539 seconds.
Compiled with NO_LAPACK=0
-------------------------
>> getenv('OPENBLAS_NUM_THREADS')
ans = 1
>> A=randn(4000);
>> tic;AA=A'*A;toc
Elapsed time is 11.7115 seconds.
>> tic;chol(AA);toc
Elapsed time is 4.24126 seconds.
>> tic;svd(A);toc
Elapsed time is 60.4084 seconds.
>> getenv('OPENBLAS_NUM_THREADS')
ans = 2
>> A=randn(4000);
>> tic;AA=A'*A;toc
Elapsed time is 6.55407 seconds.
>> tic;chol(AA);toc
Elapsed time is 2.51173 seconds.
>> tic;svd(A);toc
Elapsed time is 46.6011 seconds.
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