[petsc-users] Handling non-solution local vector data

[Mark Lohry]

1) Is there somewhere on the doc site with a single list of all examples
and what they do? As a new user I hugely appreciate all the great examples
and documentation, but it's a little unwieldy to try and find relevant
examples by navigating the function documents.

2) I'm a little unclear as to the best-practice way to handle solution/grid
related data that isn't actual solution DOFS or mesh points, and doesn't
require global communication.

Say I want to work on an (ni X nj ) cell-centered finite volume layout with
one DOF per cell. I start with

DMDACreate2d(PETSC_COMM_WORLD,
      DMDA_BOUNDARY_PERIODIC, DMDA_BOUNDARY_NONE, /* periodic in i, no conn
in j */
      DMDA_STENCIL_BOX, /* 5-point stencil */
      ni,nj, /* number of cells */
      PETSC_DECIDE,PETSC_DECIDE, /* let petsc determine number of procs */
      1, /* one degree of freedom per cell */
      1, /* stencil width */
      NULL,NULL,&da);

Now I can construct the solution vector like so:

struct Field { PetscScalar u; };
Field **soln;
Vec global_vec;
DMDACreateGlobalVector(da,&global_vec);
DMDAVecGetArray(da,global_vec,&soln); // converts global vector into
Field**

and access the local elements through soln[j][i]. But say I want to store
some grid information locally, say the FaceNormal for a cell face:
struct FaceNormal{ PetscScalar nx,ny; };
FaceNormal **IFace;

Now it seems that the CreateGlobalVector/CreateLocalVector are just going
to allocate for 1 DOF because of how the DMDA was defined, so there
wouldn't be sufficient storage for the 2 variables in FaceNormal. What's an
appropriate way to do this? Clearly I could just malloc that myself, but
it'd be nice to keep the same indexing as the petsc vectors.

Thanks in advance,
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