This post talks about MPI_Init function in MPI. MPI_Init function is called at the beginning of an MPI program to set up the communication environment for all processes in the specified communicator. Without this function, none of the MPI operations will work.

Syntax for MPI_Init

int MPI_Init( int *argc, char ***argv )

Input Parameters

• argc : Pointer to the number of arguments
• argv : Pointer to the argument vector

Example code –

#include"stdio.h"
#include"mpi.h"

int main(int argc, char **argv)
{
	int myid, size;
	
	//Initialize MPI environment 
	MPI_Init(&argc,&argv);
	
	//Get total number of processes
	MPI_Comm_size(MPI_COMM_WORLD, &size);
	
	//Get my unique ID among all processes
	MPI_Comm_rank(MPI_COMM_WORLD, &myid);
	
	printf("Hello World from %d out of %d.\n",myid, size);
	
	//End MPI environment        
	MPI_Finalize();
}

To compile this code, use following command –

mpicc hello_world.c

To execute this code, run following command –

mpiexec -n 4 ./a.out

Output of this code will be something similar to the following –


Hello World from 0 out of 4.
Hello World from 1 out of 4.
Hello World from 2 out of 4.
Hello World from 3 out of 4.

To know more about MPI, visit our dedicated page for MPI here.

If you are new to Parallel Programming / HPC, visit our dedicated page for beginners.

References :

• MPI Standard Website
• MPI_Init Syntax and other information