This example code shows the use of simple MPI_Send/MPI_Recv operations
in implementing a simple, one-dimensional decomposition of a 2-d mesh.
The code uses
<UL>
<LI>Topologies to specify neighbors
<LI>Arbitrary sized <IT>square</IT> mesh of size <TT>maxn</TT> by  
<TT>maxn</TT>
<LI>Takes at most  <TT>maxn</TT> iterations
<LI>Tests for convergence by comparing the 2-norm of the difference of the
current and previous iteration.
</UL>
<P>
There are a number of related exercises that look at many variations of the
communication step, including overlapping communication and computation.
