/* recipMPI.c - MPI version of master0/slave0.c in PVM
 * calculate the reciprocal
 * variation of greetings.c -- greetings program
 *
 * Send a message from all processes with rank != 0 to process 0.
 *    Process 0 prints the messages received.
 *
 * Input: none.
 * Output: contents of messages received by process 0.
 *
 * See Chapter 3, pp. 41 & ff in PPMPI.
 */
#include <stdio.h>
#include <string.h>
#include "mpi.h"

main(int argc, char* argv[]) {
    int         my_rank;       /* rank of process      */
    int         p;             /* number of processes  */
    int         source;        /* rank of sender       */
    int         dest;          /* rank of receiver     */
    int         tag = 0;       /* tag for messages     */
    char        message[100];  /* storage for message  */
    double      reciprocal;
    int num;
    char        name[100];     // Processor name
    int         len;           // Length of the name
    double      start_time, 
                end_time;    
    MPI_Status  status;        /* return status for    */
                               /* receive              */

    /* Start up MPI */
    MPI_Init(&argc, &argv);

    /* Find out process rank  */
    MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);

    /* Find out number of processes */
    MPI_Comm_size(MPI_COMM_WORLD, &p);
    
    MPI_Get_processor_name(name, &len);

    if (my_rank != 0) {
         source = 0; //receive from the "master process"
         MPI_Recv(&num, 1, MPI_INT, source, tag, 
                MPI_COMM_WORLD, &status);
        if (num==0)
            {reciprocal = 0.0;}
        else
            {reciprocal = 1.0 / num;}
	    
        /* Create message */
        sprintf(message, "Greetings from process %d!",
            my_rank);
        dest = 0;
	MPI_Send(&reciprocal, 1, MPI_DOUBLE,dest, tag, MPI_COMM_WORLD);
        /* Use strlen+1 so that '\0' gets transmitted */
        MPI_Send(message, strlen(message)+1, MPI_CHAR, 
            dest, tag, MPI_COMM_WORLD);
	MPI_Send(name, len+1, MPI_CHAR, 
            dest, tag, MPI_COMM_WORLD);
    } else { /* my_rank == 0 */
        start_time = MPI_Wtime();
        printf("Hello from process 0 on %s\n", name);
        for (source = 1; source < p; source++) {
	    num = source;
	    dest = source;
	    MPI_Send(&num, 1, MPI_INT,dest, tag, MPI_COMM_WORLD);
	    MPI_Recv(&reciprocal, 1, MPI_DOUBLE, source, tag, 
                MPI_COMM_WORLD, &status);
            MPI_Recv(message, 100, MPI_CHAR, source, tag, 
                MPI_COMM_WORLD, &status);
	    MPI_Recv(name, 100, MPI_CHAR, source, tag, 
                MPI_COMM_WORLD, &status);
            printf("%s on machine %s, reciprocal = %lf\n", message, name,
	            reciprocal);
        }
	end_time = MPI_Wtime();
	printf("Total time for sending/recieving data: %f\n",
	                end_time - start_time);
    }

    /* Shut down MPI */
    MPI_Finalize();
} /* main */

/*
lamboot -v hostfile

mpicc -o recipMPI recipMPI.c

mpirun N recipMPI
Hello from process 0 on helium
Greetings from process 1! on machine silicon, reciprocal = 1.000000
Greetings from process 2! on machine phosphorus, reciprocal = 0.500000
Greetings from process 3! on machine magnesium, reciprocal = 0.333333
Greetings from process 4! on machine deadend, reciprocal = 0.250000

mpirun -np 6 recipMPI
Hello from process 0 on helium
Greetings from process 1! on machine silicon, reciprocal = 1.000000
Greetings from process 2! on machine phosphorus, reciprocal = 0.500000
Greetings from process 3! on machine magnesium, reciprocal = 0.333333
Greetings from process 4! on machine deadend, reciprocal = 0.250000
Greetings from process 5! on machine helium, reciprocal = 0.200000

mpirun -np 10 recipMPI
Hello from process 0 on helium
Greetings from process 1! on machine silicon, reciprocal = 1.000000
Greetings from process 2! on machine phosphorus, reciprocal = 0.500000
Greetings from process 3! on machine magnesium, reciprocal = 0.333333
Greetings from process 4! on machine deadend, reciprocal = 0.250000
Greetings from process 5! on machine helium, reciprocal = 0.200000
Greetings from process 6! on machine silicon, reciprocal = 0.166667
Greetings from process 7! on machine phosphorus, reciprocal = 0.142857
Greetings from process 8! on machine magnesium, reciprocal = 0.125000
Greetings from process 9! on machine deadend, reciprocal = 0.111111
*/