[petsc-users] I am wondering if there is a way to implement SPMM

[Barry Smith]

  From the manual page:  Unless scall is MAT_REUSE_MATRIX C will be created.

  Since you want to use the C that is passed in you should use MAT_REUSE_MATRIX.

  Note that since your B and C matrices are dense the issue of sparsity pattern of C is not relevant.

  Barry

> On Aug 4, 2015, at 11:59 AM, Cong Li <solvercorleone at gmail.com> wrote:
> 
> Thanks very much. This answer is very helpful.
> And I have a following question.
> If I create B1, B2, .. by the way you suggested and then use MatMatMult to do SPMM. 
> PetscErrorCode  MatMatMult(Mat A,Mat B,MatReuse scall,PetscReal fill,Mat *C)
> should I use  MAT_REUSE_MATRIX for MatReuse part of the arguement. 
> 
> Thanks
> 
> Cong Li
> 
> On Wed, Aug 5, 2015 at 1:27 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> 
> > On Aug 4, 2015, at 4:09 AM, Cong Li <solvercorleone at gmail.com> wrote:
> >
> > I am sorry that I should have explained it more clearly.
> > Actually I want to compute a recurrence.
> >
> > Like, I want to firstly compute A*X1=B1, and then calculate A*B1=B2, A*B2=B3 and so on.
> > Finally I want to combine all these results into a bigger matrix C=[B1,B2 ...]
> 
>    First create C with MatCreateDense(,&C). Then call MatDenseGetArray(C,&array); then create B1 with MatCreateDense(....,array,&B1); then create
> B2 with MatCreateDense(...,array+shift,&B2) etc where shift equals the number of __local__ rows in B1 times the number of columns in B1, then create B3 with a larger shift etc.
> 
>    Note that you are "sharing" the array space of C with B1, B2, B3, ..., each Bi contains its columns of the C matrix.
> 
>   Barry
> 
> 
> 
> >
> > Is there any way to do this efficiently.
> >
> >
> >
> > On Tue, Aug 4, 2015 at 5:45 PM, Patrick Sanan <patrick.sanan at gmail.com> wrote:
> > On Tue, Aug 04, 2015 at 03:42:14PM +0900, Cong Li wrote:
> > > Thanks for your reply.
> > >
> > > I have an other question.
> > > I want to do SPMM several times and combine result matrices into one bigger
> > > matrix.
> > > for example
> > > I firstly calculate AX1=B1, AX2=B2 ...
> > > then I want to combine B1, B2.. to get a C, where C=[B1,B2...]
> > >
> > > Could you please suggest a way of how to do this.
> > This is just linear algebra, nothing to do with PETSc specifically.
> > A * [X1, X2, ... ] = [AX1, AX2, ...]
> > >
> > > Thanks
> > >
> > > Cong Li
> > >
> > > On Tue, Aug 4, 2015 at 3:27 PM, Jed Brown <jed at jedbrown.org> wrote:
> > >
> > > > Cong Li <solvercorleone at gmail.com> writes:
> > > >
> > > > > Hello,
> > > > >
> > > > > I am a PhD student using PETsc for my research.
> > > > > I am wondering if there is a way to implement SPMM (Sparse matrix-matrix
> > > > > multiplication) by using PETSc.
> > > >
> > > >
> > > > http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatMatMult.html
> > > >
> >
> 
>