question on MatMatMult

[Randall Mackie]

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
>>
>>
> 
> 
>