MPI Pi Calculation

This Program for Pi calculation depicts the usage of MPI_Wtime, MPI_Bcast and MPI_Reduce.

	/************************************************************
	This Program for Pi calculation depicts the usage of
	MPI_Wtime, MPI_Bcast and MPI_Reduce
	*************************************************************/
	#include "mpi.h"
	#include <math.h>
	#include <stdio.h>
	#define MAX_NAME 80 /* length of characters for naming a process */
	#define MASTER 0 /* rank of the master */
	int main(int argc, char *argv[])
	{
	int rank, /* rank variable to identify the process */
	nprocs, /* number of processes */
	i,
	len; /* variable for storing name of processes */
	int n = 1000; /* the number of bins */
	double PI25DT = 3.141592653589793238462643; /* 25-digit-PI*/
	double mypi, /* value from each process */
	pi, /* value of PI in total*/
	step, /* the step */
	sum, /* sum of area under the curve */
	x;
	char name[MAX_NAME]; /* char array for storing the name of each process */
	double start_time, /* starting time */
	end_time, /* ending time */
	computation_time; /* time for computing value of PI */
	/*Initialize MPI execution environment */
	MPI_Init(&argc, &argv);
	MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
	MPI_Comm_rank(MPI_COMM_WORLD, &rank);
	MPI_Get_processor_name(name, &len);
	start_time = MPI_Wtime();
	/* Broadcast the number of bins to all processes */
	/* This broadcasts an integer which is n, from the master to all processes
	* and
	*/
	MPI_Bcast(&n, 1, MPI_INT, MASTER, MPI_COMM_WORLD);
	/* Calculating for each process */
	step = 1.0 / (double) n;
	sum = 0.0;
	for (i = rank + 1; i <= n; i += nprocs)
	{
	x = step * ((double)i - 0.5);
	sum += (4.0/(1.0 + x*x));
	}
	mypi = step * sum;
	printf("This is my sum: %.16f from rank: %d name: %s\n", mypi, rank, name);
	/* Now we can reduce all those sums to one value which is Pi */
	MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
	if (rank == 0)
	{
	printf("Pi is approximately %.16f, Error is %.16f\n", pi, fabs(pi - PI25DT));
	end_time = MPI_Wtime();
	computation_time = end_time - start_time;
	printf("Time of calculating PI is: %f\n", computation_time);
	}
	/* Terminate MPI execution environment */
	MPI_Finalize();
	}

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