question on MatMatMult
Matthew Knepley
knepley at gmail.com
Mon Mar 17 18:18:47 CDT 2008
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
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