#include<stdio.h>
#include<mpi.h>
#include<stdlib.h>
#include<time.h>
#include <windows.h>

double Trap(double left_endpt, double right_endpt, int trap_count, double base_1en);
double f(double x);

int main(int argc, char* argv[]) {

    int done = 0, my_rank, comm_sz, n = 10000000, local_n;
    double a = 0.0, b = 1.0, h, local_a, local_b;
    double local_int, total_int;
    int source;
    int namelen;
    char processor_name[MPI_MAX_PROCESSOR_NAME];
    double startwtime = 0.0, endwtime;
    MPI_Init(&argc, &argv);

    MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);//进程号
    MPI_Comm_size(MPI_COMM_WORLD, &comm_sz);//进程总数
    MPI_Get_processor_name(processor_name, &namelen);//获取处理器名称 
    fprintf(stderr, "Process %d of %d on %s \n",my_rank, comm_sz, processor_name);

    while (!done) {
        if (my_rank == 0) {
            fprintf(stdout, "Enter the number of intervals: (0 quits) ");
            fflush(stdout);
            if (scanf_s("%d", &n) != 1) {
                fprintf(stdout, "No number entered; quitting\n");
                n = 0;
            }
            startwtime = MPI_Wtime();
        }
        if (n == 0)
        {
            done = 1;
        }
        else {
            h = (b - a) / n;  /* h is the same for a11 processes */ //间距
            local_n = n / comm_sz;  /* So is the number of trapezoids */ //

            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);
            //printf("localdata my_rank:%d comm_sz:%d processor_name:%s\n", my_rank, comm_sz, processor_name);
            //printf("localVar local_n:%d local_a:%f local_b:%f local_int:%f \n\n", local_n, local_a, local_b, local_int);

            if (my_rank != 0) {
                MPI_Send(&local_int, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD);
            } //发送缓冲区的起始地址，将发送的数据个数（非负整数），数据类型，目的进程标识号，消息标志，通信域
            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, our estimate\n", n);
                printf("of the integral from %f to %f = %.15e\n", a, b, total_int);
                endwtime = MPI_Wtime();
                printf("wall clock time = %f\n", endwtime - startwtime);
            }
        }
    }

    MPI_Finalize();

    return 0;
}/* main */


double Trap(
    double left_endpt,
    double right_endpt,
    int trap_count,
    double base_1en) {

    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_1en;
        estimate += f(x);
    }

    estimate = estimate * base_1en;
    return estimate;
}/*Trap*/

double f(double x) {
    return x * x;
}

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