comm_split 奇怪的行为？

Question

我花了相当多的时间试图解决这个问题，所以我终于来这里寻求帮助。我正在学习 mpi，问题是因为我是新人，所以我不知道为什么会发生一些奇怪的行为。我想做的是我有 8 个数字分布在 8 个处理器上，如下所示。然后我拆分通信器，然后从子通信器交换元素，如下所示:

0 1 2 3 4 5 6 7

分割

0 1 2 3 | 4 5 6 7

交换

2 3 0 1 | 6 7 4 5

输出是 4 5 6 7 0 1 2 3 但输出应该是 2 3 0 1 6 7 4 5。我可以得到一些帮助来了解为什么它给我这个奇怪的结果吗？

#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
#include <math.h>
int main(argc,argv)
int argc;
char *argv[];

{
    int myid, numprocs;
    int color,Zero_one,new_id,new_nodes;
    MPI_Comm NEW_COMM; 
    MPI_Init(&argc,&argv);
    MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
    MPI_Comm_rank(MPI_COMM_WORLD,&myid);


    int my_num, my_received;

       int old_id;


    switch(myid){

        case 0:
            my_num = 0;
            old_id = 0;

        break;


        case 1:
            my_num = 1;
            old_id = 1;

        break;

        case 2:
            my_num = 2;
            old_id = 2;

        break;

        case 3:
            my_num = 3;
            old_id = 3;

        break;

        case 4:
            my_num = 4;
            old_id = 4;

        break;

        case 5:
            my_num = 5;
            old_id = 5;

        break;

        case 6:
            my_num = 6;
            old_id = 6;

        break;

        case 7:
            my_num = 7;
            old_id = 7;

        break;


    }

//here i split

    color=myid % 2;
    MPI_Comm_split(MPI_COMM_WORLD,color,myid,&NEW_COMM);
    MPI_Comm_rank( NEW_COMM, &new_id);
    MPI_Comm_rank( NEW_COMM, &new_nodes);



  //here i exchange in the sub list or communicator

        if(new_id < 2){

            MPI_Send(&my_num, 1, MPI_INT,  2 + new_id, 0, NEW_COMM);
            MPI_Recv(&my_received, 1, MPI_INT, 2 + new_id, 0, NEW_COMM, MPI_STATUS_IGNORE);         

        }
        else
        {
            MPI_Recv(&my_received, 1, MPI_INT, new_id - 2, 0, NEW_COMM, MPI_STATUS_IGNORE);         
            MPI_Send(&my_num, 1, MPI_INT, new_id - 2 , 0, NEW_COMM);


        }



    printf("old_id= %d received num= %d\n", old_id, my_received);


    MPI_Finalize();

}

Answer 1

运行你的程序我得到:

old_id= 4 received num= 0
old_id= 5 received num= 1
old_id= 1 received num= 5
old_id= 3 received num= 7
old_id= 6 received num= 2
old_id= 7 received num= 3
old_id= 0 received num= 4
old_id= 2 received num= 6

根据您的分配，所有偶数排名均收集在一个通信器中，所有赔率收集在另一个通信器中:

old_id= 0 received num= 4
old_id= 2 received num= 6
old_id= 4 received num= 0
old_id= 6 received num= 2

和:

old_id= 1 received num= 5
old_id= 3 received num= 7
old_id= 5 received num= 1
old_id= 7 received num= 3

这看起来像你要求的东西。要么我无法重现您的问题，要么误解了它，要么没有任何问题？