c++ - 使用 mpi 的谐波和：开始使用 mpi 时遇到问题，不确定如何将其修改为谐波级数

Question

我是使用 MPI 的新手，我正在尝试修改此代码以执行 n = 20 的谐波系列，但我不太确定如何开始。MPI 究竟是如何工作的，我们如何对其进行修改。提示：修改 sum.cpp 程序，计算 sum = 1 + 1/2 + 1/3 + 1/4 + … 1/n！让 n = 20

#include "mpi.h"
    #include <cstdio>
    #include <cmath>
    #include <cstdlib>
    
    #define ARRAY_SIZE 1000000
    
    int main (int argc,  char *argv[]) {
    
       int myid, numprocs;
       int namelen;
       int* numbers = new int[ARRAY_SIZE];
       char processor_name[MPI_MAX_PROCESSOR_NAME];
    
       MPI_Init(&argc, &argv);
       MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
       MPI_Comm_rank(MPI_COMM_WORLD, &myid);
       MPI_Get_processor_name(processor_name, &namelen);
     
       printf("Process %d on %s\n", myid, processor_name);
     
       for (int i=0; i<ARRAY_SIZE; i++)
          numbers[i] = i;  //could be randomly generated
    
       int s = (int)floor(ARRAY_SIZE/numprocs);
       int s0 = s + ARRAY_SIZE%numprocs;
    
       int startIndex = s0 + (myid-1)*s;
       int endIndex = startIndex + s;
    
       double startwtime;
       if (myid == 0) {
          startwtime = MPI_Wtime();
       }
    
       int i;
       int part_sum = 0;
       
       if (myid == 0) {
          // master worker - comput the master's numbers
          for (i=0; i<s0; i++) {
             part_sum += numbers[i];
          }
          printf("Process %d - startIndex 0 endIndex %d; part_sum %ld\n",
                 myid, s0-1, part_sum);
       } else {
          //slave's work
          for (i= startIndex; i<endIndex; i++) {
             part_sum += numbers[i];
          }
          printf ("Process %d - startIndex %d endIndex %d; part_sum %ld\n",
                  myid, startIndex, endIndex-1, part_sum);
       }
    
       int sum = 0;
       MPI_Reduce(&part_sum, &sum, 1, MPI_INT, MPI_SUM, 0, MPI_COMM_WORLD);
    
       if (myid == 0) {
          double runTime = MPI_Wtime() - startwtime;
          printf("Execution time (sec) = %f sum = %ld \n",
                 runTime, sum);
       }
    
       delete[] numbers;
    
       MPI_Finalize();
    }

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