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

[Kumar Appaiah]

On Sat, Feb 13, 2010 at 03:20:19PM +0100, Sylvestre Ledru wrote:
> severity 569436 normal
> thanks
> 
> Hello,
> 
> I installed a chroot (through debootstrap) and I don't have the problem.

Did you try rebuilding libitpp on amd64? Did it FTBFS for you? 

> With the intel code, I get:
>  Left singular vectors (stored columnwise)
>  ( -0.86, -0.00) (  0.40, -0.00) (  0.32,  0.00)
>  ( -0.35,  0.13) ( -0.24, -0.21) ( -0.63,  0.60)
>  (  0.15,  0.32) (  0.61,  0.61) ( -0.36,  0.10)
> 
> The code is working fine with Octave or Scilab.

Thanks for checking. Did you use amd64? Did you notice that the FTBFS
is on amd64?

> Sylvestre
> PS: I changed the severity to "normal".
> FYI, grave means:
> "makes the package in question unusable or mostly so, or causes data
> loss, or introduces a security hole allowing access to the accounts of
> users who use the package."

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.

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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