Thanks Matt, I'll look into these.
Randy Matthew Knepley wrote: > On Mon, Mar 17, 2008 at 6:03 PM, Randall Mackie <rlmackie862 at gmail.com> > wrote: >> >> Matthew Knepley wrote: >> > On Mon, Mar 17, 2008 at 5:28 PM, Randall Mackie <rlmackie862 at >> gmail.com> 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. > > I found > > > http://links.jstor.org/sici?sici=0036-1429(199604)33%3A2%3C555%3ATSMFTB%3E2.0.CO%3B2-8 > > http://citeseer.ist.psu.edu/13843.html > > > http://links.jstor.org/sici?sici=0036-1429(197806)15%3A3%3C556%3AAOTBEB%3E2.0.CO%3B2-E > > Matt > >> Randy >> >> >> > >> > Matt >> > >> >> Thanks, Randy >> >> > > >
