MPI_Gatherv函数的使用

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#include "mpi.h"#include<stdio.h>int main(int argc,char **argv){//每个进程发送100＊150矩阵的第rank列的前（100－rank）个数//stride要>=rcounts［i]      int gsize;int rank;      int *rbuf,*displs,stride;      int sendarray[100][150],*sptr;int *rcounts;      int root=0;MPI_Datatype stype;        stride=102;        for(int i=0;i<100;i++)for(int j=0;j<150;j++)sendarray[i][j]=i*150+j;MPI_Init(&argc,&argv);MPI_Comm_size(MPI_COMM_WORLD,&gsize);MPI_Comm_rank(MPI_COMM_WORLD,&rank);rbuf=(int*)malloc(gsize*stride*sizeof(int));displs=(int*)malloc(gsize*sizeof(int));      rcounts=(int*)malloc(gsize*sizeof(int));for(int i=0;i<gsize;i++){displs[i]=i*stride;      rcounts[i]=100-i;}      //create the datatype for the column to be sent      MPI_Type_vector(100-rank,1,150,MPI_INT,&stype);MPI_Type_commit(&stype);      /*sptr is the address of the start of rank column*/       sptr=&sendarray[0][rank];MPI_Gatherv(sptr,1,stype,rbuf,rcounts,displs,MPI_INT,root,MPI_COMM_WORLD);       if(rank==0){for(int i=0;i<gsize;i++){               int k=0;               for(int j=displs[i];k<rcounts[i];k++)                   printf("%d\n",rbuf[j+k]);                  }           }MPI_Finalize();                         }

用MPI_Type_struct的等效实现

MPI_UB type allows the user to easily set the end of the structure
if you define a structure datatype and wish to send or receive multiple items,
you should explicitly include an MPI_UB entry as the last member of the structure
当定义某个结构体，并且需要发送或接收该结构体的多个项时，为了对齐与填充的需要，
需要显示指定MPI_UB的项作为该结构体的最后一个成员

#include "mpi.h"#include<stdio.h>int main(int argc,char **argv){//每个进程发送100＊150矩阵的第rank列的前（100－rank）个数//stride要>=rcounts［i]      int gsize;int rank;      int *rbuf,*displs,stride;      int sendarray[100][150],*sptr,disp[2],blocklen[2];int *rcounts;      int root=0;MPI_Datatype stype,type[2];        stride=102;        for(int i=0;i<100;i++)for(int j=0;j<150;j++)sendarray[i][j]=i*150+j;MPI_Init(&argc,&argv);MPI_Comm_size(MPI_COMM_WORLD,&gsize);MPI_Comm_rank(MPI_COMM_WORLD,&rank);rbuf=(int*)malloc(gsize*stride*sizeof(int));displs=(int*)malloc(gsize*sizeof(int));      rcounts=(int*)malloc(gsize*sizeof(int));for(int i=0;i<gsize;i++){displs[i]=i*stride;      rcounts[i]=100-i;}      //create the datatype for one int ,with extent of entire row      blocklen[0]=1,blocklen[1]=1;      disp[0]=0,disp[1]=150*sizeof(int);      type[0]=MPI_INT,type[1]=MPI_UB;      MPI_Type_struct(2,blocklen,disp,type,&stype);MPI_Type_commit(&stype);      /*sptr is the address of the start of rank column*/      sptr=&sendarray[0][rank];MPI_Gatherv  (sptr,100-rank,stype,rbuf,rcounts,displs,MPI_INT,root,MPI_COMM_WORLD);       if(rank==0){for(int i=0;i<gsize;i++){               int k=0;               for(int j=displs[i];k<rcounts[i];k++)                   printf("%d\n",rbuf[j+k]);                  }           }MPI_Finalize();                         }