LAPACK Archives

[Lapack] shall we update B22 in DHGEQZ for the 2x2 block when B22 is neg



Hi,

I read the LAPACK forum. There is one topic which is not followed for more
than 3 years.  (bug0026)

http://www.netlib.org/lapack/Errata/index.html#_strong_span_class_red_bug0026_span_strong_problem_when_playing_with_dgeev_and_gfortran_optimization_flags

Firstly, the abstract is misleading. The problems occurs in DGGEV but not
DGEEV.

When I run a simple test using the same input data, LAPACK 3.4.0 failed
too. Then I print out some intermediate output in the related subroutine.
There may be one issue in DHGEQZ. At line 912-923 (for 2x2 block), it
multiply -1 to the last column of H and T. But I think we should also
update B22 too. B22 is still used below with the output of DLAG2(H, T). If
it doesn't update B22, it may generate zero B1R/B1I/B2R/B2I at line
1019-1026.

*
*           If B22 is negative, negate column ILAST
*
            IF( B22.LT.ZERO ) THEN
               DO 210 J = IFRSTM, ILAST
                  H( J, ILAST ) = -H( J, ILAST )
                  T( J, ILAST ) = -T( J, ILAST )
  210          CONTINUE
*
               IF( ILZ ) THEN
                  DO 220 J = 1, N
                     Z( J, ILAST ) = -Z( J, ILAST )
  220             CONTINUE
               END IF
            END IF
*
Once I add B22 = -B22 in the above code, I can got correct output for those
3 omega. My LAPACK 3.4.0 is compiled by gfortran with -O3 on Fedora16_x86.

Best Regards!
Peng HongBo
-------------- next part --------------
An HTML attachment was scrubbed...
URL: 
http://lists.eecs.utk.edu/mailman/private/lapack/attachments/20120401/2bc67e1e/attachment.html
 

<Prev in Thread] Current Thread [Next in Thread>


For additional information you may use the LAPACK/ScaLAPACK Forum.
Or one of the mailing lists, or