[petsc-users] matrix-matrix addition
Boyce Griffith
griffith at cims.nyu.edu
Mon Sep 27 00:56:03 CDT 2010
I am trying to compute a matrix A that is of the form:
A = B + P^t C P
using MatPtAP and MatAXPY. The call to MatAXPY is very slow ---
presumably because I haven't allocated the correct nonzero structure. I
can easily determine the nonzero structures of B, C, and P, but I do not
think that I can easily compute the nonzero structure of P^t C P
(although I can compute its nonzero structure with some difficulty).
Is it possible to add extra non-zero locations to an existing matrix?
Or should I try to extract the nonzero structures of B and P^t C P to
pre-allocate A correctly? (Or am I overlooking some functionality in
PETSc that will do most of this for me?)
A tangentially related question is: is there any way to find out the
actual fill (or fill ratio) following a call to MatPtAP?
Thanks in advance for any suggestions!
-- Boyce
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