This is a two processor example. Each processor owns one box in the grid. For reference, the two grid boxes are those in the example diagram in the struct interface chapter of the User's Manual. Note that in this example code, we have used the two boxes shown in the diagram as belonging to processor 0 (and given one box to each processor). The solver is PCG with no preconditioner.
We recommend viewing examples 1-4 sequentially for a nice overview/tutorial of the struct interface.