Question

我真的是MPI的菜鸟。我只需要完成我的大学任务。有人能帮助我吗？

任务是在N * M矩阵中找到最小值和最大值。进程计数必须等于N.我尝试使用MPI_Reduce查找最小值和最大值但我得到错误结果。这是我的代码。

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

const int n = 5;
const int m = 4;

void fill_matrix_randomly(int matrix[n][m], int max_value);
void write_matrix(int matrix[n][m]);
int find_max(int* vector, int vector_size);
int find_min(int* vector, int vector_size);
void write_vector(int* vector, int vector_size);

int main(int argc, char* argv[])
{
    int my_rank = 0;
    int comm_size = 0;

    int a[n][m];
    int receive_buffer[m];
    int partial_max[m];
    int partial_min[m];

    MPI_Init(&argc, &argv);

    MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
    MPI_Comm_size(MPI_COMM_WORLD, &comm_size);

    if (comm_size != n)
    {
        printf("Please set process count = %d and run again.", n);
        MPI_Finalize();
        return 0;
    }

    if (my_rank == 0)
    {
        fill_matrix_randomly(a, 10);
        write_matrix(a);    
    }
    /* MPI Scatter(address of send buffer, number of elements sent to each process, data type of send buffer, address of receive buffer, number of elements in receive buffer, data type of receive buffer, rank of sending process, communicators space) */
    MPI_Scatter(a, n, MPI_INT, receive_buffer, n, MPI_INT, 0, MPI_COMM_WORLD);
    /* MPI_Reduce(address of send buffer, address of receive buffer, number of elements in send buffer, data type of elements in send buffer, reduce operation, rank of root process, communicators space) */
    MPI_Reduce(receive_buffer, partial_max, n, MPI_INT, MPI_MAX, 0, MPI_COMM_WORLD);
    MPI_Reduce(receive_buffer, partial_min, n, MPI_INT, MPI_MIN, 0, MPI_COMM_WORLD);
    if (my_rank == 0)
    {
        printf("Vector of partial max values.\n");
        write_vector(partial_max, n);
        printf("Vector of partial min values.\n");
        write_vector(partial_min, n);

        int max = find_max(partial_max, n);
        int min = find_min(partial_min, n);
        printf("Matrix boundaries = [%d..%d]\n", min, max);
    }
    MPI_Barrier(MPI_COMM_WORLD);
    MPI_Finalize();

    return 0;
}

int find_max(int* vector, int vector_size)
{
    int max = vector[0];
    int i = 0;  
    for (i = 0; i < vector_size; i++)
    {
        if (vector[i] > max)
        {
            max = vector[i];
        }       
    }
    return max;
}

int find_min(int* vector, int vector_size)
{
    int min = vector[0];
    int i = 0;
    for (i = 0; i < vector_size; i++)
    {
        if (vector[i] < min)
        {
            min = vector[i];
        }
    }
    return min;
}

void fill_matrix_randomly(int matrix[n][m], int max_value)
{
    int i = 0;
    int j = 0; 
    srand(time(NULL));
    for (i = 0; i < n; i++)
    {
        for (j = 0; j < m; j++)
        {
            matrix[i][j] = rand() % max_value;
        }
    }   
}

void write_matrix(int matrix[n][m])
{
    int i = 0;
    int j = 0;
    for (i = 0; i < n; i++)
    {
        for (j = 0; j < m; j++)
        {
            printf("%4d", matrix[i][j]);            
        }
        printf("\n");
    }
}

void write_vector(int* vector, int vector_size)
{
    int i = 0;
    for (i = 0; i < vector_size; i++)
    {
        printf("vector[%d] = %d\n", i, vector[i]);
    }
}

这是输出。

$ mpiexec -n 5 ./main
   8   1   3   9
   1   0   3   1
   4   9   5   5
   1   7   4   9
   8   5   7   4
Vector of partial max values.
vector[0] = 9
vector[1] = 8
vector[2] = 5
vector[3] = 9
vector[4] = 16
Vector of partial min values.
vector[0] = -1
vector[1] = -1
vector[2] = -1
vector[3] = -1
vector[4] = 1
Matrix boundaries = [-1..16]

我哪里错了？我应该改变什么？我花了一整天的时间来寻找解决方案。

Answer 1

您的矩阵是n行m列。当您将此矩阵分发到n进程时，每个进程都必须处理m个元素，而是在所有向量调用中使用n计数。您应该传递m的长度：

MPI_Scatter电话;
MPI_Reduce次来电;
write_vector次来电;
find_max和find_min来电。

请注意，您已正确声明receive_buffer，partial_max，partial_min为m元素。

在矩阵MPI中查找最小值和最大值

1 个答案: