LAPACK Archives

[Lapack] [lapackers] bug in DGEHRD

The balancing is choosing to scale some rows/columns by factors like 1e18,
which rather amplifies tiny rounding errors in the (presumably correctly)
computed eigenvectors of the balanced matrix, when balancing is undone 
at the end.
The expert driver interface dgeevx would let the user disable balancing, 
until
we figure out whether this is a bug or a feature, I'm not sure which.

Jim

Julien Langou wrote:

We have a bug report at:
http://icl.cs.utk.edu/lapack-forum/viewtopic.php?f=2&t=1818
It comes from Numpy guys.

The matrix is very pretty to look at with a lots of zero and a lots of 
structure but DGEHRD does not seem to like, not one little bit. See post.

Note that while
   [V,D]=eig(A);
does not work,
   [Q,H]=hess(A);
   [V,D]=eig(H);
   V = Q*V;
works ...

Ideas?

Best wishes,
Julien.





<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