[Numpy-discussion] Zero row in SVD's unitary matrix on some Mac's
Jason Grout
jason-sage at creativetrax.com
Tue Apr 26 12:22:46 EDT 2011
On 4/26/11 11:12 AM, Jason Grout wrote:
> On 4/26/11 11:07 AM, Jason Grout wrote:
>> And indeed, I get a 0 row as the last row of the V**H matrix
>
> I just double-checked things one last time and saw that I actually
> hadn't changed the first argument of zgesdd to "A" in the program that I
> actually ran. So with this change, I get a nonzero last row of the V**H
> matrix from the C call to zgesdd. So everything is consistent between
> the C call to zgesdd and the numpy svd call.
>
> So now my remaining question is: if the Lapack docs only say that V**H
> is the full n-by-n matrix if M>=N, why is numpy returning it even if M<N?
One more post talking to myself...
I notice that the zgesvd routine docs guarantee that the V returned is
unitary, regardless of the size of A. So this might be another argument
for calling zgesvd instead of zgesdd.
Thanks,
Jason
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