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 > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener
