[Octave-bug-tracker] [bug #55564] GESDD: vastly different singular values when vectors are also requested

[Dmitri A. Sergatskov]

Follow-up Comment #7, bug #55564 (project octave):

May be we should revisit bug 49940.
It looks to me that gesvd mostly runs single-thread 
even with multithreaded blas. 

I run a simple benchmark and watched top. With 
gesdd cpuload was 400% (4 threads), with 
gesvd it started ~400% but  dropped quickly to 100%



LD_PRELOAD=/usr/lib64/libopenblaso.so OMP_NUM_THREADS=4 ./run-octave 

octave:1> a=randn(3000);
octave:2> tic; [u2,s2,v2] = svd (a); toc
Elapsed time is 13.4637 seconds.
octave:3> svd_driver("gesvd")
octave:4> tic; [u2,s2,v2] = svd (a); toc
Elapsed time is 247.86 seconds.



similar results with liopenblasp (pthread interface) and atlas.

I am not sure if this is octave problem (posted results in 49940
did not show such a big difference), or lapack's.

Dmitri.


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