MPI - 發送數組的片段

Question

所以我有一個雙打數組。我希望每5分鐘發送一次，以便接收進程。所以基本上，我需要一種發送特定雙打的方式，在它們之間邁進。除了將雙打存儲到發送緩衝區之外，是否有這樣的功能？製作我自己的派生類型會更好嗎？

Answer 1

您應該創建一個MPI數據類型;它給人的MPI庫的機會，以避免額外的副本從數組編組，這是非常簡單的使用做，在這種情況下，MPI_Type_vector()：

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

int main(int argc, char** argv) 
{ 
    int size, rank; 
    const int bigsize=50; 
    const int stride = 5; 
    const int count = (bigsize + stride - 1)/stride; 

    const int sender = 0; 
    const int receiver = 1; 
    const int mytag = 1; 

    MPI_Init(&argc,&argv); 
    MPI_Comm_size(MPI_COMM_WORLD,&size); 
    MPI_Comm_rank(MPI_COMM_WORLD,&rank); 

    if (size < 2) { 
     fprintf(stderr,"%s: Require at least two processors.\n", argv[0]); 
     MPI_Finalize(); 
     exit(-1); 
    } 


    if(rank == sender) 
    { 
     double bigarray[bigsize]; 
     for (int i=0; i<bigsize; i++) 
      bigarray[i] = 0.; 

     for (int i=0; i<bigsize; i+=stride) 
      bigarray[i] = i/stride; 

     printf("[%d]: ", rank); 
     for (int i=0; i<bigsize; i++) 
      printf("%lf ", bigarray[i]); 
     printf("\n"); 

     MPI_Datatype everyfifth; 

     MPI_Type_vector(count, 1, stride, MPI_DOUBLE, &everyfifth); 
     MPI_Type_commit(&everyfifth); 

     MPI_Send(bigarray, 1, everyfifth, receiver, mytag, MPI_COMM_WORLD); 

     MPI_Type_free(&everyfifth); 
    } 
    else if(rank == receiver) 
    { 
     double littlearray[count]; 

     MPI_Status status; 

     MPI_Recv(littlearray, count, MPI_DOUBLE, sender, mytag, 
        MPI_COMM_WORLD, &status); 

     printf("[%d]: ", rank); 
     for (int i=0; i<count; i++) 
      printf("%lf ", littlearray[i]); 
     printf("\n"); 
    } 

    MPI_Finalize(); 

    return 0; 
} 

編譯和運行提供了

$ mpicc -o vector vector.c -std=c99 
$ mpirun -np 2 ./vector 
[0]: 0.000000 0.000000 0.000000 0.000000 0.000000 1.000000 0.000000 0.000000 0.000000 0.000000 2.000000 0.000000 0.000000 0.000000 0.000000 3.000000 0.000000 0.000000 0.000000 0.000000 4.000000 0.000000 0.000000 0.000000 0.000000 5.000000 0.000000 0.000000 0.000000 0.000000 6.000000 0.000000 0.000000 0.000000 0.000000 7.000000 0.000000 0.000000 0.000000 0.000000 8.000000 0.000000 0.000000 0.000000 0.000000 9.000000 0.000000 0.000000 0.000000 0.000000 
[1]: 0.000000 1.000000 2.000000 3.000000 4.000000 5.000000 6.000000 7.000000 8.000000 9.000000