#include <stdio.h>

#include "mpi.h"

#define N 10                             //N是阶乘求和的项数

double calculate(int x)                  //该函数计算整数x的阶乘

double factorial(int k,int l);            //计算分段k到l的阶乘倒数之和

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

{

    int nprocs,myrank;

    double a = 0,b = N;

    double res0,res,a0,b0;

    MPI_Init(&argc,&argv);

    MPI_Comm_size(MPI_COMM_WORLD,&nprocs);

    MPI_Comm_rank(MPI_COMM_WORLD,&myrank);

a0 = a + (myrank + 0) * (b - a)/nprocs;   //计算本进程的积分区间

    b0 = a0 + (b - a)/nprocs -1;

    res0 = factorial(a0,b0);

    MPI_Reduce(&res0,&res,1,MPI_DOUBLE,MPI_SUM,0,MPI_COMM_WORLD);

    printf("the final result is %0.16lf",res);

    MPI_Finalize();

    return 0;

}

double factorial(int k,int l){

    double sum = 0;

    for(int i = k;i <= l;i++){

        sum = sum+1.0/calculate(i);

    }

    return sum;

}

double calculate(int x)

{

    int i;

    int result = 1;

    if (x == 0) { result = 1;}

    else for (i = 1;i <= x;i++) {

       result = result * i;

    }

    return result;

}