On 4/25/11 12:57 PM, Pauli Virtanen wrote:
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.
I was just looking up the documentation for ZGESDD and noticed that the value we have for rwork in the numpy call [1] does not match the Lapack docs. This was changed in Lapack 3.2.2 [2]. I've submitted a pull request: https://github.com/numpy/numpy/pull/78 but I have not tested the change. I doubt this fix will fix the problem on this thread, but it makes sense to make the change anyway. Thanks, Jason [1] https://github.com/numpy/numpy/blob/master/numpy/linalg/linalg.py#L1300 [2] http://icl.cs.utk.edu/lapack-forum/viewtopic.php?f=2&t=1779, or http://www.netlib.org/lapack/lapack-3.2.2.html (bug 0046)