Hello World program in mpi

                           In this post, we will see Hello World program in MPI.

                           For How to install MPI on Linux (Ubuntu and Fedora), check following link: 

https://www.comrevo.com/2019/10/How-to-install-MPI-on-Linux-Ubuntu-and-Fedora.html
               





Program (helloworldmpi.c)

#include "mpi.h" int main(int argc, char **argv) {    int rank, size;    MPI_Init(&argc,&argv);    MPI_Comm_rank(MPI_COMM_WORLD, &rank);    MPI_Comm_size(MPI_COMM_WORLD, &size);    printf("Hello world! Process of rank %d out of %d processes.\n",rank,size);    MPI_Finalize();    return 0; }

 
Output:

>>> mpic++ helloworldmpi.c  >>> mpirun -np 5 ./a.out Hello world! Process of rank 0 out of 5 processes. Hello world! Process of rank 2 out of 5 processes. Hello world! Process of rank 3 out of 5 processes. Hello world! Process of rank 1 out of 5 processes. Hello world! Process of rank 4 out of 5 processes.

  

Note:

                     Here, 5 is the number of processes. We compile program by mpic++. We get object file a.out. Then, we run it on many processes (in this example 5). 

                     Function MPI_Comm_rank() gives rank of process. Ranks are in the range 0 to n-1.

                     Function MPI_Comm_size() gives number of processes.