On 10/19/2011 10:29 AM, Umut Tabak wrote:
Dear all,
I have run into a problem today with the gmm++ library. I am not very
sure where the problem could be. I coded a symmetric lanczos solver
for my problem and used gmm++ and MUMPS (as the linear solver).
However, the accuracy of the basic linear algebra operations
matrix-vector product and gmm::add, scale and so seem to be
questionable to me.
Well it could be a bit cryptic to understand for you, maybe, but let
me rephrase with an example:
I am computing some coefficients to form a tridiagonal matrix and
these coefficients that I compute in gmm++ start to deviate from the
ones I computed in MATLAB. They seem to be the same at the starting
iterations then conducting these matrix-vector operations(for
orthogonalizations), they start to diverge, I am not sure what the
problem could be.
I went over my code several times, however, the end results tell me
that there is indeed a problem in the orthogonalization phase, which
is basically a combination of matrix-vector operations.
Any comments are appreciated on this issue.
Best regards,
Umut
As a reply to my own post, there is definitely a problem in the linear
algebra operations in gmm++ from accuracy point of view.
I tested my problem with MTL4 and the results seem to be far more close
to what they should be.
I am not sure what the problem is in gmm++ but this deserves some
attention.
I can provide a test case in MATLAB and gmm++ where I compare these
tridiagonal coefficients of the lanczos proces. To test the MATLAB code,
one should have the MUMPS MATLAB interface installed.
Best regards,
Umut
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