[petsc-users] Vec Set DM and Mat Set DM

[Sun, Hui]

If I have a DM object with dof=3. So in each grid point, there are 3 components. Now if I set a Mat according to this DM object, I have something like: 
MatSetValuesStencil(jac,1,&row,5,col,v,INSERT_VALUES);

What shall I put in col? Usually I should have something like: 
col[0].i = i;   col[0].j = j-1;   col[1].i = i;   col[1].j = j;   etc  ...

But now I want to do something like:
col[0].i.u = i;   col[0].j.u = j-1;   col[0].i.v = i;   col[0].j.v = j-1;   col[0].i.p = i;   col[0].j.p = j-1;   etc  ...

What is the right syntax for doing this?

After setting up the stencils I want to call:
MatSetValuesStencil(jac,1,&row,15,col,v,INSERT_VALUES);

Should I put 15 as the number of columns being entered. (5 point stencil, 3 degrees of freedom in each point)

Best,
Hui
________________________________________
From: Jed Brown [jed at jedbrown.org]
Sent: Saturday, June 21, 2014 11:28 AM
To: Sun, Hui; petsc-users at mcs.anl.gov
Subject: Re: [petsc-users] Vec Set DM and Mat Set DM

"Sun, Hui" <hus003 at ucsd.edu> writes:

> I'm thinking about defining a distributed Vec using grid information. The usual way to do that is to call VecCreateMPI, or VecCreate and VecSetSizes. However, that does not necessarily distribute Vec according to the grid information, DM. I'm thinking of doing something like:
>
> ierr = DMDAGetInfo(da,0,&mx,&my,0,0,0,0,0,0,0,0,0,0);CHKERRQ(ierr);
>
> ierr = DMDAGetCorners(da,&xs,&ys,NULL,&xm,&ym,NULL);
>
>
> and then define the Vec according to (xs,ys,xm,ym).

Use DMCreateGlobalVector() and DMCreateLocalVector().