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