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

double f(double x) {
	return 4/(1+x*x);
}

double Trap (double left_endpt, double right_endpt, int trap_count, double base_len) {
	double estimate, x;
	int i;

	estimate = (f(left_endpt) + f(right_endpt))/2.0;
	for (i = 1; i<=trap_count-1; i++) {
		x = left_endpt + i*base_len;
		estimate+=f(x);
	}
	estimate = estimate*base_len;

	return estimate;
}

int main(void) {
	int my_rank, comm_sz, n=100000000, local_n;
	double a=0.0, b=1.0, h, local_a, local_b;
	double local_int, total_int;
	int source;

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

	h=(b-a)/n;
	local_n=n/comm_sz;

	local_a=a+my_rank*local_n*h;
	local_b=local_a+local_n*h;
	local_int=Trap(local_a, local_b, local_n, h);

	if (my_rank!=0) {
		MPI_Send(&local_int, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD);
	} else {
		total_int = local_int;
		for (source=1; source<comm_sz; source++) {
			MPI_Recv(&local_int, 1, MPI_DOUBLE, source, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
			total_int += local_int;
		}
	}

	if(my_rank==0)  {
		printf("with n = %d trapezoids, or estimate\n", n);
		printf("of the integral form %f to %f = %.15e\n", a, b, total_int);
	}
	MPI_Finalize();
	return 0;
}
 

MPI執行效果圖

VC6執行效果圖