On Mon, Mar 17, 2008 at 5:28 PM, Randall Mackie <rlmackie862@xxxxxxxxx> wrote:If I want to compute H = L^T L where L is a sparse matrix which is an approximation to the laplacian, and hence H is the biharmonic (also sparse), and if I have L as an MPI matrix in PETSc, will MatMatMult work for this (assuming I create the transpose of L first).
In other words, does MatMatMult look at the non-zero structure only that would result, or does it think the result is a dense matrix?
It builds the structure dynamically, which explains the "fill" argument. This is not a great thing to do unless you have no idea how to form it directly.
I know how to form the Laplacian (that's easy) but I do not know how to form the biharmonic directly, on a non-uniform grid. If anyone knows how, other than direct multiplication, and can point me in the right direction, that would be most appreciated.
Randy
Matt
Thanks, Randy