[Trilinos-Users] EpetraExt MatrixMatrix
Kevin Long
kevin.long at ttu.edu
Tue Jun 1 17:23:29 MDT 2010
Hi,
Vicki Howle and I have encountered a problem for which we want to compute
explicitly (as an Epetra_CrsMatrix) the product B^T D B, where D is a
diagonal matrix. We have B as an Epetra_CrsMatrix and diag(D) as an
Epetra_Vector.
We can do this easily enough by making an Epetra_CrsMatrix representation of
D, then calling EpetraExt::MatrixMatrix::Multiply() twice, first to form
C1=D*B, then again to form C= B^T C1. The second call can use
transposeA=true so we don't need to form B^T.
Alternatively, I could form C1=sqrt(D) B, then do C1^T C1. Again, not hard to
write.
However, neither approach takes advantage of the fact that D is diagonal,
which means (a) I need to construct a whole Epetra_CrsMatrix for something
that can really just be stored as a vector, and (b) inside
MatrixMatrix::Multiply(), I'm doing needless work to find the graph of the
product D B when I already know that D B and B will have the same graph.
The operation B^T D B is a fairly common; any chance that someone will extend
MatrixMatrix to provide an optimized multiply for that case? Or better yet,
has anyone already written such code?
Thanks,
Kevin
--
------------------------------------------------------
Kevin Long
Associate Professor
Department of Mathematics and Statistics
Texas Tech University
Lubbock, TX
"The end of fear is the beginning of wisdom"
-- Bertrand Russell
------------------------------------------------------
More information about the Trilinos-Users
mailing list