[Numpy-discussion] Zero row in SVD's unitary matrix on some Mac's

Pauli Virtanen pav at iki.fi
Mon Apr 25 13:57:33 EDT 2011

On Mon, 25 Apr 2011 10:16:13 -0700, Rob Beezer wrote:
> Many more details and complete transcripts are at:
> http://trac.sagemath.org/sage_trac/ticket/11248
> Any thoughts or advice to help us understand this would be greatly
> appreciated.

The Numpy routine is a very thin wrapper of LAPACK's ZGESDD, and probably 
cannot have any bugs of this kind, so the problem is most likely with the 
LAPACK and BLAS libraries you use. You will probably be able to reproduce 
the problem also with an equivalent Fortran/C snippet calling LAPACK 

Problems like this in BLAS/LAPACK are somewhat difficult to track. You 
could try switching to another BLAS library (or, if you use ATLAS, 
compile it differently) and checking if the problem disappears.

Pauli Virtanen

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