[petsc-users] DMComposite and Matrix construction

[Barry Smith]

  DMCreateMatrix() ? 


> On Jul 28, 2015, at 9:02 PM, Gideon Simpson <gideon.simpson at gmail.com> wrote:
> 
> I’m working with a DMComposite where I have a DMRedundant with 2 parameters, and then a standard DMDACreate with some number of entires that I would like to have distributed.  For concreteness, suppose it is 
> 
> DMCompositeCreate(PETSC_COMM_WORLD, &packer);
> DMRedundantCreate(PETSC_COMM_WORLD, 0, 2, &p_dm);
> DMCompositeAddDM(packer,p_dm);
> DMDACreate1d(PETSC_COMM_WORLD,DM_BOUNDARY_NONE, nx, 1, 1, NULL,&u_dm);
> DMCompositeAddDM(packer,u_dm);
> DMCreateGlobalVector(packer,&U);
> 
> Now, I would like to construct a matrix for this problem that can be used for computing Jacobians in a nonlinear solve.  Is there a way to get the matrix size to layout in a “useful” way, in the sense that the first process, which owns the two degrees of freedom of p_dm and the first N0 number of the rows of u_dm, controls the corresponding N0+2 rows of the matrix, and analgously for the second process has the next N1 rows of the u_dm vector, and has the next N1 rows of the matrix?
> 
> -gideon
>