[petsc-users] submatrix times subvector

[Tabrez Ali]

Thanks! I will try this.

Tabrez

On 01/15/2013 12:23 PM, Jed Brown wrote:
> On Tue, Jan 15, 2013 at 12:09 PM, Tabrez Ali <stali at geology.wisc.edu 
> <mailto:stali at geology.wisc.edu>> wrote:
>
>     Jed
>
>     The problem with MatGetSubMatrix is that iscol isn't available
>     easily. I want to get all associated columns but according to the
>     man page it is not possible in Fortran.
>
>     "If iscol is PETSC_NULL then all columns are obtained (not
>     supported in Fortran)."
>
>
> Well, we could add Fortran support for that case (it currently needs a 
> custom binding to do that) or you can
>
> call MatGetColumnOwnershipRange(A,colstart,colend,ierr)
> ncols = colend - colstart
> call ISCreateStride(comm,ncols,colstart,one,iscol,ierr)
>
> and pass iscol to MatGetSubMatrix(). This is what's done internally 
> when you pass iscol=NULL:
>
>   if (!iscol) {
>     ierr = 
> ISCreateStride(((PetscObject)mat)->comm,mat->cmap->n,mat->cmap->rstart,1,&iscoltmp);CHKERRQ(ierr);
>
>
>     Is there a workaround?
>
>     Tabrez
>
>
>     On 01/14/2013 03:38 PM, Jed Brown wrote:
>>     On Mon, Jan 14, 2013 at 3:27 PM, Tabrez Ali
>>     <stali at geology.wisc.edu <mailto:stali at geology.wisc.edu>> wrote:
>>
>>         Hello
>>
>>         I am solving a system of equations of the form:
>>
>>         |A C| |u1| = |f1|
>>         |C'B| |u2|   |f2|
>>
>>         After each solve, I need to perform B*f2 before updating f.
>>         Should I use MatGetSubMatrix/VecGetSubVector followed by
>>         MatMult or is there something simpler.
>>
>>
>>     Yes, or let PCFIELDSPLIT do all the block solver stuff for you.
>
>
>     -- 
>     No one trusts a model except the one who wrote it; Everyone trusts an observation except the one who made it- Harlow Shapley
>
>

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