在矩阵MPI中查找最小值和最大值

Question

我真的很喜欢MPI的东西。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矩阵中查找最小值和最大值。进程计数必须等于N.我尝试使用MPI_Reduce来查找最小值和最大值，但是我得到错误结果。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]); 
    } 
} 

这里是输出。

$ 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] 

我在哪里错了？我应该改变什么？我花了整整一天的时间寻找解决方案。

Answer 1

您的矩阵是n行m列。当您将此矩阵分配到n进程时，每个进程必须处理m元素，但是在所有向量调用中使用的计数为n。您应通过长度为m的：

• MPI_Scatter调用;
• 均为MPI_Reduce来电;
• 均为write_vector调用;
• find_max和find_min调用。

注意，您必须正确声明receive_buffer，partial_max，partial_min是m元素。