[SciPy-Dev] LAPACK problems with *gges wrappers

[Skipper Seabold]

On Thu, May 3, 2012 at 1:14 PM, Denis Laxalde <denis at laxalde.org> wrote:
>
> Skipper Seabold a écrit :
> > Can someone take a look at the comments on this pull request [1]? I'm
> > unable to replicate the failures and it's unclear to me that there are
> > problems with the python code and the fortran wrappers.
>
> I can confirm the tests failures:
>
>
>  ======================================================================
>  ERROR: test_qz_double (test_decomp.TestQZ)
>  ----------------------------------------------------------------------
>  Traceback (most recent call last):
>    File
> "/home/denis/.local/lib/python2.7/site-packages/scipy/linalg/tests/test_decomp.py",
> line 1645, in test_qz_double
>      AA,BB,Q,Z = qz(A,B)
>    File
> "/home/denis/.local/lib/python2.7/site-packages/scipy/linalg/_decomp_qz.py",
> line 168, in qz
>      overwrite_b=overwrite_b, sort_t=sort_t)
>  error: (lwork>=MAX(1,8*n+16)||lwork==-1) failed for 6th keyword lwork:
> dgges:lwork=46
>
>  ======================================================================
>  ERROR: test_qz_double_sort (test_decomp.TestQZ)
>  ----------------------------------------------------------------------
>  Traceback (most recent call last):
>    File
> "/home/denis/.local/lib/python2.7/site-packages/scipy/linalg/tests/test_decomp.py",
> line 1705, in test_qz_double_sort
>      AA,BB,Q,Z,sdim = qz(A,B,sort=sort)
>    File
> "/home/denis/.local/lib/python2.7/site-packages/scipy/linalg/_decomp_qz.py",
> line 168, in qz
>      overwrite_b=overwrite_b, sort_t=sort_t)
>  error: (lwork>=MAX(1,8*n+16)||lwork==-1) failed for 6th keyword lwork:
> dgges:lwork=40
>
>  ======================================================================
>  ERROR: test_qz_single (test_decomp.TestQZ)
>  ----------------------------------------------------------------------
>  Traceback (most recent call last):
>    File
> "/home/denis/.local/lib/python2.7/site-packages/scipy/linalg/tests/test_decomp.py",
> line 1634, in test_qz_single
>      AA,BB,Q,Z = qz(A,B)
>    File
> "/home/denis/.local/lib/python2.7/site-packages/scipy/linalg/_decomp_qz.py",
> line 168, in qz
>      overwrite_b=overwrite_b, sort_t=sort_t)
>  error: (lwork>=MAX(1,8*n+16)||lwork==-1) failed for 6th keyword lwork:
> sgges:lwork=46
>
>  ----------------------------------------------------------------------
>
> Lapack 3.3.1, Atlas 3.8.4 from Debian.
>
>

Thanks. Can you check again with pushed fix?

I think the documentation is wrong and the actual minimum value for
lwork should be max(8*n, 6*n+16) and not the 8*n+16 in the
documentation.

If anyone cares to double check my reading of the source.

http://www.netlib.no/netlib/lapack/double/dgges.f

Skipper