采用 MPI_Send 和 MPI_Recv 编写代码来实现 MPI_Allgather 的功能

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MPI_Allgather实现

#include "stdio.h"#include "mpi.h"int main( int argc, char* argv[] ){    int i;    int rank, nproc;    int isend, irecv[32];    double start_time, end_time, time, cputime;             MPI_Init( &argc, &argv );    start_time = MPI_Wtime();MPI_Comm_size( MPI_COMM_WORLD, &nproc );    MPI_Comm_rank( MPI_COMM_WORLD, &rank );    isend = rank + 1;    MPI_Allgather(&isend, 1, MPI_INT, irecv, 1, MPI_INT,                              MPI_COMM_WORLD);    for(i=0; i<nproc; i++)         printf("My rank =  %d  irecv = %d\n", rank, irecv[i]);        end_time = MPI_Wtime();    cputime = end_time - start_time;    MPI_Reduce(&cputime,&time,1,MPI_DOUBLE,MPI_SUM,0,MPI_COMM_WORLD);    if(rank == 0)    printf("time is %f s.\n",time/nproc);    MPI_Finalize();    }

采用 MPI_Send 和 MPI_Recv 编写代码来实现

#include "time.h"#include "stdio.h"#include "mpi.h"int main(int argc,char * argv[]){    int i;    int rank, nproc;    int send, recv[32];    MPI_Status status;    double start_time, end_time, time, cputime;            MPI_Init( &argc, &argv );    start_time = MPI_Wtime();    MPI_Comm_size( MPI_COMM_WORLD, &nproc );    MPI_Comm_rank( MPI_COMM_WORLD, &rank );       send = rank + 1;    for(i=0;i<nproc;i++){MPI_Send(&send,1,MPI_INT,i,rank,MPI_COMM_WORLD);    }    for(i=0;i<nproc;i++){MPI_Recv(recv+i,1,MPI_INT,i,i,MPI_COMM_WORLD,&status);    }        for(i=0; i<nproc; i++)         printf("My rank =  %d  recv = %d\n", rank, recv[i]);    end_time = MPI_Wtime();    cputime = end_time - start_time;    MPI_Reduce(&cputime,&time,1,MPI_DOUBLE,MPI_SUM,0,MPI_COMM_WORLD);    if(rank == 0)    printf("time is %f s.\n",time/nproc);    MPI_Finalize();}

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