Create a pure diagonal matrix

[Matthew Knepley]

Using a combination of Jacobi and KSP scaling, you almost never need a
diagonal matrix in solves. However, if you really do, I would just use
MatDiagonScale():

http://www-unix.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/Mat/MatDiagonalScale.html#MatDiagonalScale

and if you really need to, you can wrap that operation in a MatShell.

   Matt

On Mon, Mar 31, 2008 at 4:11 PM, Shi Jin <jinzishuai at yahoo.com> wrote:
>
> Hi,
>
> I have a related question to the one above: what is the best way to create a
> purely diagonal matrix?
> I am using
> ierr = MatCreateMPIAIJ(comm,localM,localN,PETSC_DETERMINE,PETSC_DETERMINE,1,
> PETSC_NULL, 0, PETSC_NULL, &lumpedMP);CHKERRQ(ierr);
> But I would think there might be a even better (faster/less memory) way?
>
> I thought about the BDiag Matrix. I tried
> ierr=MatCreateMPIBDiag(comm,localM,globalSize,globalSize,PETSC_NULL,1,
> PETSC_NULL,PETSC_NULL,&lumpedM);CHKERRQ(ierr);
> but not sure if it is done correctly. I am a little suspicious about those
> pointers I set as NULL.
>
> If the above two are both correct, is there a better one?
>
> Thank you very much.
>  --
> Shi Jin, PhD
>
>
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What most experimenters take for granted before they begin their
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