#11248: SVD matrix decomposition may return a non-invertible "unitary" matrix
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Reporter: rbeezer | Owner: jason, was
Type: defect | Status: new
Priority: major | Milestone: sage-4.7
Component: linear algebra | Keywords:
Work_issues: | Upstream: N/A
Reviewer: | Author:
Merged: | Dependencies:
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Comment(by rbeezer):
Here is what I heard back from the `NumPy` discussion list:
"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 also found a FORTRAN example, coincidentally a 3 x 4:
http://software.intel.com/sites/products/documentation/hpc/mkl/lapack/mkl_lapack_examples/zgesdd_ex.f.htm
Otherwise, I think this one is now beyond me.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11248#comment:13>
Sage <http://www.sagemath.org>
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