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

[Pauli Virtanen]

On Mon, 25 Apr 2011 10:16:13 -0700, Rob Beezer wrote:
[clip]
> 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 
directly.

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