PPT Slide
MPI_Comm_size( MPI_COMM_WORLD, &size );
if (size != 4) MPI_Abort( MPI_COMM_WORLD, 1 );
/* xlocal[][0] is lower ghostpoints, xlocal[][maxn+2] is upper */
/* Note that top and bottom processes have one less row of interior
if (rank == 0) i_first++;
if (rank == size - 1) i_last--;
/* Fill the data as specified */
for (i=1; i<=maxn/size; i++)
xlocal[i_first-1][j] = -1;
xlocal[i_last+1][j] = -1;