MAIN_ENV;
/* define message tags */
#define ROW 99
#define DIFF 98
#define DONE 97
int main( int argc , char ** argv )
{
int pid , P, done, i , j, N;
float tempdiff , local_diff , temp, **A;

MAIN_INITENV;
GET_PID( pid );
GET_NUMPROCS(P);
N = atoi ( argv [1]);
tempdiff = 0.0;
done = 0;
A = (double **) malloc ((N/P+2) * sizeof (float *));
for ( i =0; i < N/P+2; i ++) {
A[ i ] = (float *) malloc ( sizeof (float) * (N+2));
}
initialize(A);

while (!done) {
local_diff = 0.0;
/* MPI_CHAR means raw byte format */
if ( pid ) { /* send my first row up */
SEND(&A[1][1], N* sizeof (float), MPI_CHAR, pid-1, ROW);
}
if ( pid != P-1) { /* recv last row */
RECV(&A[N/P+1][1], N* sizeof (float), MPI_CHAR, pid+1, ROW);
}
if ( pid != P-1) { /* send last row down */
SEND(&A[N/P][1], N* sizeof (float), MPI_CHAR, pid+1, ROW);
}
if ( pid ) { /* recv first row from above */
RECV(&A[0][1], N* sizeof (float), MPI_CHAR, pid-1, ROW);
}
for ( i =1; i <= N/P; i ++) for (j=1; j <= N; j++) {
temp = A[ i ][j];
A[ i ][j] = 0.2 * (A[ i ][j] + A[ i ][j-1] + A[i-1][j] + A[ i ][j+1] + A[i+1][j]);
local_diff += fabs (A[ i ][j] - temp);
}