Hej Peng,
The 2x2 blocks should only appear in real arithmetic (S/D) and then
they correspond to complex conjugate pairs of eigenvalues for
real matrix pairs (A, B). The complex generalized Schur form (C/Z) should
be upper triangular and you can read of the eigenvalues from the pairs
(s_ii, t_ii) where s_ii and tii are diagonal entries (complex numbers) of
the generalized Schur form S  sT (= Q^T (AsB) Z ).
What type of code are you developing and for what architecture(s)?
How big are the problems you are trying to solve?
Best wishes,
Bo K?gstr?m
Hi,
I am working on GGEV code. But I found ZGGEV failed to converge in one
sample. I found it is similar to what has been reported in this
mailinglist. Do we have any update for this problem?
_http://icl.cs.utk.edu/lapackforum/archives/lapack/msg00535.html_
With more debug print output, I think ZHGEQZ failed to converge
because it can't get eigenvalue for the 2x2 block. There is a
difference between DHGEQZ and ZHGEQZ. DHGEQZ has special code to
handle the 2x2 block but ZHGEQZ doesn't. Is there any special
consideration about this in C/ZHGEQZ? As what I found in debug output,
the implicit sweep doesn't change the 2x2 block (H is 2x2 and T is 2x2
upper triangular) even with exceptional shift. So it failed to converge.
Best Regards!
Peng HongBo
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