Scattering context options
Barry Smith
bsmith at mcs.anl.gov
Fri Jul 27 12:17:34 CDT 2007
Graham,
It seems unlike the matrix was preallocated; this will
definitely slow things down a great deal. Pluse you have a
scatter for each row, this is fundamentally not scalable.
Barry
On Fri, 27 Jul 2007, Graham Kells wrote:
> Hi ,
>
> I'm scattering from a global vector (used as a kind of look up table) to a
> bunch of local vectors and then using the values in the local vectors as
> indices to populate a global matrix.
> The basic population routine goes something like this
>
> do myrow=Istart,Iend-1
>
> ! Returns column indices of full matrix for rowindex list(myrow+1)
> call getrow(list(myrow+1),rowCOO,colCOO,valCOO)
> call ISCreateGeneral(PETSC_COMM_WORLD,n,(colCOO-1),from,ierr)
> call ISCreateGeneral(PETSC_COMM_SELF,n,idx_to-1,to,ierr) call
> VecScatterCreate(vlist,from,outvec,to,scatter,ierr)
> call
> VecScatterBegin(scatter,vlist,outvec,INSERT_VALUES,SCATTER_FORWARD,ierr)
> call VecScatterEnd(scatter,vlist,outvec,INSERT_VALUES,SCATTER_FORWARD,ierr)
> call VecScatterDestroy(scatter,ierr)
> call ISDestroy(from,ierr)
> call ISDestroy(to,ierr)
>
> call VecGetValues(outvec,n,idx_to-1,idx_real,ierr)
> idx_from=int(idx_real)
>
>
> call MatSetValues(A,1,myrow,n,idx_from-1,valCOO,INSERT_VALUES,ierr)
>
> end do
>
> While this works, it is prohibitively slow. Any ideas on why this is? Of
> course if you can suggest a better way of doing this that would be great.
>
> Supposing you can't and I want to experiment with different MPI communication
> modes within the scatter context. How do specify the MPI_Ssend option, for
> example?
>
> Thanks in advance,
>
> Graham
>
>
>
>
>
>
>
>
>
>
>
>
More information about the petsc-users
mailing list