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我正在尝试使用 MPI 在 N 个进程中划分 2D 矩阵的列。对于模板，我使用了MPI_Scatter 上的示例 - 发送 2D 数组的列。

我的代码：

//HEADERS
    char** board_initialize(int n, int m)
    {
        int k, l;

        char* bd = (char*)malloc(sizeof(char) * n * m);
        char** b = (char**)malloc(sizeof(char*) * n);
        for (k = 0; k < n; k++)
            b[k] = &bd[k * m];

        for (k = 0; k < n; k++)
            for (l = 0; l < m; l++)
                b[k][l] = rand() < 0.25 * RAND_MAX;

        return b;
    }

    void board_print(char** b, int n, int m)
    {
        int k, l;

    //  system("@cls||clear");
        for (k = 0; k < n; k++)
        {
            for (l = 0; l < m; l++)
                printf("%d", b[k][l]);
            printf("\n");
        }
        printf("\n");
    }


    int main(int argc, char* argv[])
    {   
        int N = 10;
        int i, j;

        char * boardptr = NULL;                 // ptr to board
        char ** board;                          // board, 2D matrix, contignous memory allocation!

        int procs, myid;            
        int mycols;
        char ** myboard;                        // part of board that belongs to a process

        MPI_Init(&argc, &argv);                 // initiailzation
        
        MPI_Comm_rank(MPI_COMM_WORLD, &myid);   // process ID
        MPI_Comm_size(MPI_COMM_WORLD, &procs);  // number of processes

        // initialize global board
        if (myid == 0)
        {
            srand(1573949136);
            board = board_initialize(N, N);
            boardptr = *board;
            board_print(board, N, N);
        }
        // divide work
        mycols = N / procs;


        // initialize my structures
        myboard = board_initialize(N,mycols);

        MPI_Datatype column_not_resized, column_resized;
        MPI_Type_vector(N, 1, N, MPI_CHAR, &column_not_resized);
        MPI_Type_commit(&column_not_resized);
        MPI_Type_create_resized(column_not_resized, 0, 1*sizeof(char), &column_resized);
        MPI_Type_commit(&column_resized);

        // scatter initial matrix
        MPI_Scatter(boardptr, mycols, column_resized, *myboard, mycols, column_resized, 0, MPI_COMM_WORLD);
        MPI_Barrier(MPI_COMM_WORLD);

        board_print(myboard, N, mycols);
        
        MPI_Finalize();         // finalize MPI

        return 0;
    }

整个板子看起来像：

0000010010
0100000000
0000101100
0101000010
1000000100
0000010010
0000001110
0110000100
0000100000
0100010010

如果我使用 2 个进程，我希望每个进程都会得到一半（第一个进程列 1-5 和第二个进程列 6-10）。但是，如果我打印这两个过程的myboard，我会得到一些奇怪的结果：

proc0:       proc1:
0 0 0 0 0    1 0 0 1 0 
0 0 1 0 0    0 0 0 1 1 
0 1 0 0 0    0 0 0 0 0 
0 1 0 0 0    0 1 0 1 0 
0 0 0 0 1    0 1 1 0 0 
0 1 1 0 0    0 0 1 0 0 
0 1 0 1 0    0 0 0 1 0 
0 0 0 0 1    0 0 1 0 0 
1 0 0 0 0    0 0 1 0 0 
0 1 0 0 0    0 1 0 0 0

这可能是一些愚蠢的错误，但我似乎无法找到它。任何帮助将非常感激。<3

注意：proc1 的输出可能只是一些垃圾，因为每次运行我都会得到不同的输出。

4

1 回答 1

0

您忘记区分发送和接收类型，即 的参数MPI_Type_vector将取决于适当的类型。您需要执行以下操作：

MPI_Datatype acol, acoltype, bcol, bcoltype;
if (myid == 0) {
    MPI_Type_vector(N, 1, N, MPI_CHAR, &acol);
    MPI_Type_commit(&acol);
    MPI_Type_create_resized(acol, 0, 1*sizeof(char), &acoltype);
}
MPI_Type_vector(N, 1, mycols, MPI_CHAR, &bcol);
MPI_Type_commit(&bcol);
MPI_Type_create_resized(bcol, 0, 1*sizeof(char), &bcoltype);
MPI_Type_commit(&bcoltype);
MPI_Scatter (boardptr, mycols, acoltype, *myboard, mycols, bcoltype, 0, MPI_COMM_WORLD);

从发送方的角度来看，您希望创建N块（即N 行），大小为 1，步长为N（即N 列）。因此：

MPI_Type_vector(N, 1, N, MPI_CHAR, &acol);

从接收方的角度来看，您希望创建N块（即N 行），大小为 1，步长为mycols （即mycols 列）。因此：

MPI_Type_vector(N, 1, mycols, MPI_CHAR, &bcol);

旁注你确实需要 MPI_Barrier 在 MPI_Scatter 之后，因为后者已经是一个阻塞调用。

最终代码如下所示：

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

    char** board_initialize(int n, int m)
    {
        int k, l;

        char* bd = (char*)malloc(sizeof(char) * n * m);
        char** b = (char**)malloc(sizeof(char*) * n);
        for (k = 0; k < n; k++)
            b[k] = &bd[k * m];

        for (k = 0; k < n; k++)
            for (l = 0; l < m; l++)
                b[k][l] = rand() < 0.25 * RAND_MAX;

        return b;
    }

    void board_print(char** b, int n, int m)
    {
        int k, l;

    //  system("@cls||clear");
        for (k = 0; k < n; k++)
        {
            for (l = 0; l < m; l++)
                printf("%d", b[k][l]);
            printf("\n");
        }
        printf("\n");
    }


   int main(int argc, char* argv[])
    {   
        int N = 10;
        int i, j;

        char * boardptr = NULL;                 // ptr to board
        char ** board;                          // board, 2D matrix, contignous memory allocation!

        int procs, myid;            
        int mycols;
        char ** myboard;                        // part of board that belongs to a process

        MPI_Init(&argc, &argv);                 // initiailzation
        
        MPI_Comm_rank(MPI_COMM_WORLD, &myid);   // process ID
        MPI_Comm_size(MPI_COMM_WORLD, &procs);  // number of processes

        // initialize global board
        if (myid == 0)
        {
            srand(1573949136);
            board = board_initialize(N, N);
            boardptr = *board;
            board_print(board, N, N);
        }
        // divide work
        mycols = N / procs;


        // initialize my structures
        myboard = board_initialize(N,mycols);
    MPI_Datatype acol, acoltype, bcol, bcoltype;

    if (myid == 0) {
            MPI_Type_vector(N,    
                1,                  
                N,         
                MPI_CHAR,       
                &acol);       
                MPI_Type_commit(&acol);
            MPI_Type_create_resized(acol, 0, 1*sizeof(char), &acoltype);
    }
    MPI_Type_vector(N,    
               1,                  
               mycols,         
               MPI_CHAR,       
               &bcol);       

    MPI_Type_commit(&bcol);
    MPI_Type_create_resized(bcol, 0, 1*sizeof(char), &bcoltype);
    MPI_Type_commit(&bcoltype);
    

    MPI_Scatter (boardptr, mycols, acoltype, *myboard, mycols, bcoltype, 0, MPI_COMM_WORLD);
        board_print(myboard, N, mycols);
        
        MPI_Finalize();         // finalize MPI

        return 0;
    }

或者，在 IMO 中更容易的是按行而不是按列划分，代码如下所示：

int myrows = N / procs;
myboard = board_initialize(myrows, N);
MPI_Scatter (boardptr, myrows, MPI_CHAR, *myboard, myrows, MPI_CHAR, 0, MPI_COMM_WORLD);
board_print(myboard, myrows, N);
于 2021-05-03T12:49:21.643 回答