#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 jason):
Short update: I've been posting my debugging to the numpy thread:
http://mail.scipy.org/pipermail/numpy-discussion/2011-April/056099.html
Basically, it appears that the Lapack docs only guarantee that the V
matrix is unitary if the number of rows is >= number of columns in the
zgesdd function, which is what numpy calls. So I think numpy is making a
mistake calling zgesdd and returning the results if rows < columns.
Instead, they should call zgesvd, which does return a unitary V, according
to the Lapack docs. Note: when I say V, I mean V**H or whatever is
returned.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11248#comment:26>
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