[petsc-users] question about DA

[Jed Brown]

On Sat, Aug 27, 2011 at 16:09, Likun Tan <likunt at andrew.cmu.edu> wrote:

> the size of temp and H is 9*9*201, the size of S is 9*9.
>
> I used 2 processors, the returned values are
> temp: 0 0 0 9 9 101
> temp: 0 0 101 9 9 100
>

temp is partitioned in the z direction. Each processor holds the full 9x9
cross-section of the "rod".


> H: 0 0 101 9 9 100
> S: 0 5 101 9 4 100
>

The 9x9 cross-section is partitioned. The value of zs and p are just left
over from the earlier call, so they don't mean anything here.


>
> I am not sure what you mean by how DAs were constructed, the command i
> used for construction is:
> DACreate2d(PETSC_COMM_WORLD, DA_NONPERIODIC, DA_STENCIL_STAR, 9, 9,
> PETSC_DECIDE, PETSC_DECIDE, 1, 0, PETSC_NULL, PETSC_NULL, &da2D);
> DACreate3d(PETSC_COMM_WORLD, DA_NONPERIODIC, DA_STENCIL_STAR, 9, 9, 201,
> PETSC_DECIDE, PETSC_DECIDE, PETSC_DECIDE, 1, 0, PETSC_NULL, PETSC_NULL,
> PETSC_NULL, &da3D);
>

You can prevent PETSc from partitioning in the z-direction by changing the
"p" parameter from PETSC_DECIDE to 1:

DACreate3d(PETSC_COMM_WORLD, DA_NONPERIODIC, DA_STENCIL_STAR, 9, 9, 201,
PETSC_DECIDE, PETSC_DECIDE, 1, 1, 0, PETSC_NULL, PETSC_NULL,
PETSC_NULL, &da3D);
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