/* file: time.c
   compile: cc time.c -lmpi
   run: mpirun -np 4 ./a.out
*/

#include "mpi.h" 
#include <stdio.h>
main( argc, argv ) 
int argc; 
char **argv; 
{ 
    int myrank; 

    int a[10000];
    int i;
    int x[800];
    int n;
    double before, after;

    MPI_Init( &argc, &argv ); 
    MPI_Comm_rank( MPI_COMM_WORLD, &myrank ); 
    MPI_Comm_size( MPI_COMM_WORLD, &n ); 

    for (i=0; i<800; i++){
      x[i]=myrank+i;
    }
    before = MPI_Wtime();
    MPI_Gather(x, 800, MPI_INT, a, 800, MPI_INT, 0, MPI_COMM_WORLD);
    after = MPI_Wtime();
    if (myrank == 0){
      printf("time = %5f\n", (float)(after-before));
/*
      for (i=0; i<n; i++){
	for (j=0; j<800; j++) printf("%2d ", a[800*i+j]);
	printf("\n");
      }
      printf("\n");
*/
    }
      
    MPI_Finalize(); 
  }