[Pkg-scicomp-devel] Bug#569436: lapack: zgesvd seems to give incorrect results

[Kumar Appaiah]

On Sat, Feb 13, 2010 at 08:57:38AM -0600, Kumar Appaiah wrote:
> Thanks for being pedantic without providing any alternate suggestions,
> but without SVD, I'd say most of the math related packages are
> unusable, since they give absurdly wrong results. But I won't play a
> severity ping-pong although at least my work and my package(s) are
> affected.
> 
> And, I just created a fresh amd64 chroot, and Octave gives me this:
> 
> octave3.2:1> A = [1, 2, 3;4 5 6; 7 8 9]* 1j
> A =
> 
>    0 + 1i   0 + 2i   0 + 3i
>    0 + 4i   0 + 5i   0 + 6i
>    0 + 7i   0 + 8i   0 + 9i
> 
> octave3.2:2> [U, S, V] = svd(A)
> U =
> 
>   -0.00000 - 0.88741i  -0.00000 - 0.88723i  -0.39566 - 0.10061i
>    0.00000 - 0.25007i  -0.00000 - 0.24964i   0.79131 + 0.20122i
>    0.00000 + 0.38726i   0.00000 + 0.38794i  -0.39566 - 0.10061i
> 
> S =
> 
> Diagonal Matrix
> 
>    1.6848e+01            0            0
>             0   1.0684e+00            0
>             0            0   1.0403e-15
> 
> V =
> 
>   -0.47967 - 0.00000i   0.77669 + 0.00000i   0.40825 + 0.00000i
>   -0.57237 - 0.00000i   0.07569 - 0.00000i  -0.81650 + 0.00000i
>   -0.66506 + 0.00000i  -0.62532 + 0.00000i   0.40825 - 0.00000i
> 
> octave3.2:3> U*S*V'
> ans =
> 
>     0.0000 +  6.4354i    0.0000 +  8.4858i    0.0000 + 10.5362i
>    -0.0000 +  1.8138i   -0.0000 +  2.3914i   -0.0000 +  2.9689i
>     0.0000 -  2.8078i   -0.0000 -  3.7031i   -0.0000 -  4.5985i
> 
> Some help as to how to debug this package would be appreciated, since,
> even according to your "definition" above, several packages are
> unusable for me, and the bug is "grave" for me. I would really
> appreciate some further pointers in finding where the issue is.

In addition, the problem disappears if Atlas is installed; Octave
pulls in Atlas due to some recommendations, I guess. Removing Atlas
and retrying it it shows the problem on my amd64 chroot in Octave
again.

Thanks.

Kumar
-- 
In this playhouse of infinite forms I have had my play, and here have
I caught sight of him that is formless.
- Rabindranath Tagore (Gitanjali, 1912)
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