MPIプログラミング:最も簡単な基本関数を用いてPI値を計算する

#include<mpi.h>
#include<stdio.h>
#include<math.h>
#pragma comment(lib,"mpi.lib")

#define N 1000000000

int main(int argc, char **argv)
{
	
	double local = 0, pi, w, temp;
	int i, rank, size,k;
	w = 1.0 / N;
	MPI_Init(&argc, &argv);
	MPI_Comm_rank(MPI_COMM_WORLD, &rank);
	MPI_Comm_size(MPI_COMM_WORLD, &size);
	MPI_Status status;
	double t1, t2;
	t1 = MPI_Wtime();
	for (i = rank; i < N; i = i + size)
	{		
		temp = (i + 0.5)*w;
		local = 4.0 / (1.0 + temp*temp) + local;
	}	
	if ((rank!=0))
		
		MPI_Send(&local, 1, MPI_DOUBLE, 0, rank, MPI_COMM_WORLD);
	
	if (rank == 0)
	for (i = 1; i < size;i++)
	{
		MPI_Recv(&temp, 1, MPI_DOUBLE,i, i, MPI_COMM_WORLD, &status);
		local += temp;
	}
if (rank == 0)
		pi = local;
	
	t2 = MPI_Wtime();
	//t = t2 - t1;
	if (rank == 0)
	{
		printf("pi is %lf
", pi*w);
		printf("time is %lf
", t2-t1);

	}
	MPI_Finalize();	
	return 0;
}