[petsc-users] interpolate staggered grid values in parallel

[Bishesh Khanal]

Dear all,
I'm solving a system using petsc and I get a global Vec, say X . It uses
DMDA with 4 dofs (3 velocity + 1 pressure). X contains velocity at the cell
faces since I solve using staggered grid.
Now I'd like to create one array for velocity with values at cell centers
and another array for pressure (not the Vec so that I can send the pointer
to the array to other part of the code that does not use Petsc).

Currently what I do is :
------ Vec               X, X_local;
------ PetscScalar  *X_array;

// Scatter X to X_local and then use:

------- VecGetArray(X_local, &X_array)

And then have a function, say
getVelocityAt(x, y, z, component) {
// interpolate velocity at (x,y,z) cell center using X_array
}

The function getVelocityAt() gets called from outside petsc in a loop over
all (x,y,z) positions.
This is not done in parallel.

Now, how do I use Petsc to instead interpolate the cell center velocities
in parallel and store it
in an array say
PetscScalar *X_array_cellCenter;
?
This would need to have size one less along each axis compared to the
orginal DMDA size.
This way I intend to return X_array_cellCenter to the code outside Petsc.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20141125/0c2913c2/attachment.html>