An Application Example

   
 
 
The example in figure An Application Example
 shows how the grid definition and 
inquiry functions can be used in an application program. A partial 
differential equation, for instance the Poisson equation, is to be 
solved on a rectangular domain. 
First, the processes organize themselves in a two-dimensional 
structure. Each process then inquires about the ranks of its 
neighbors in the four directions (up, down, right, left). 
The numerical problem is solved by an iterative method, the details 
of which are hidden in the subroutine  relax. 
 
In each relaxation step each process computes new values for the solution grid 
function at all points owned by the process. Then the values at inter-process 
boundaries have to be exchanged with neighboring processes.  For example, the 
exchange subroutine might contain a call like 
 MPI_SEND(...,neigh_rank(1),...) to send updated values to the 
left-hand neighbor  (i-1,j).   

Set-up of process structure for two-dimensional parallel Poisson solver.