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I'm having trouble getting the correct number of processes to output on a hello world program. I'm fairly certain this program should work since it was provided by the textbook that we are using. The code is as follows: 

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

const int MAX_STRING = 100;

int main(int argc, char * argv[])
{
    char greeting[MAX_STRING];
    int comm_sz;
    int my_rank;

    MPI_Init(NULL, NULL);
    MPI_Comm_size(MPI_COMM_WORLD, &comm_sz);
    MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);

   if (my_rank != 0)
   {
       sprintf(greeting, "Greetings from process %d of %d!\n", my_rank, comm_sz);
       MPI_Send(greeting, strlen(greeting)+1, MPI_CHAR, 0, 0, MPI_COMM_WORLD);
   }
   else
   {
       printf("Greetings from process %d of %d!\n", my_rank, comm_sz);
       for (int q = 1; q < comm_sz; q++)
       {
           MPI_Recv(greeting, MAX_STRING, MPI_CHAR, q, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
           printf("%s\n", greeting);
       }
    }
    MPI_Finalize();
    return 0;
}

I am compiling it by running 

mpicxx hello_mpi.cpp -O3

Which compiles fine, then I execute it by 

mpiexec -n 4 ./a.out

Using 4 as an example number of threads. I should be receiving an output as 

Greetings from process 0 of 4!
Greetings from process 1 of 4!
Greetings from process 2 of 4!
Greetings from process 3 of 4!

But instead I am getting 

Greetings from process 0 of 1!
Greetings from process 0 of 1!
Greetings from process 0 of 1!
Greetings from process 0 of 1!

I'm not sure why I'm getting this result instead of a rank from each thread. Again, this was the code provided by the textbook we are using (although originally written in C, I tried compiling an executing in C but ran into the same error).

Any ideas?

auranykh
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0 Answers0