#include <mpi.h>
#include <stdio.h>
#include <stdlib.h>

#define RandMax 0x7FFFFFFF


int main(int argc, char *argv[])
{
    int i;
    double startwtime, endwtime;
    int myid, namelen, numprocs;
    int *a;
	int *b;
	int sum, procsum;
    int Size, subarraysize;
    MPI_Status status;
    char processor_name[MPI_MAX_PROCESSOR_NAME];

    MPI_Init(&argc, &argv);
    MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
    MPI_Comm_rank(MPI_COMM_WORLD, &myid);
    MPI_Get_processor_name(processor_name,&namelen);
    fprintf(stderr,"Process %d on %s\n", myid, processor_name);

	Size = atoi(argv[1]);
	subarraysize = Size/numprocs;

	if (myid == 0)
	{
		a = (int *)malloc(Size * sizeof(int));
		printf("The size of the sub-arrays is %d\n", subarraysize);
		sum = 0;
		for (i=0; i<Size; i++)
			a[i] = rand()%10;

		for (i=0; i<10; i++)
			printf("%5d", a[i]);
		printf("\n");

		startwtime = MPI_Wtime();
		for (i=1; i<numprocs; i++)
		{
			MPI_Send(&a[i*subarraysize], subarraysize, MPI_INT, i, 17, MPI_COMM_WORLD);
		}
		for (i=0; i<subarraysize; i++)
			sum += a[i];
		printf("sum in master is %d\n", sum);
		for (i=1; i<numprocs; i++)
		{
			MPI_Recv(&procsum, 1, MPI_INT, MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &status);
//			sum += procsum;
			printf ("One of the partial sums is %d\n", procsum);
		}
		endwtime = MPI_Wtime();
		printf("Wall clock time: %f\n", endwtime-startwtime);
	//	printf("The grand total is: %d\n", sum);
	}
	else
	{
		sum = 0;
		b = (int *)malloc(subarraysize * sizeof(int));
		MPI_Recv(b, subarraysize, MPI_INT, 0, 17, MPI_COMM_WORLD, &status);
		for (i=0; i<subarraysize; i++)
			sum += b[i];
		MPI_Send(&sum, 1, MPI_INT, 0, 17, MPI_COMM_WORLD);
	}
	MPI_Finalize();
	return 0;
}