Thread: Another MPI question

in the code below. I use MPI_Comm_excl to exclude rank 0 of MPI_COMM_WORLD
and then split the remaining ranks in "buckets" and correspond a communicator. I use Allreduce in order to sum the workersid (after excluding rank 0 and before splitting) and spread the results (And seems that works). But now I am trying to build an intercommunicator between the excluding rank 0 and the spitting "buckets".

MPI_Intercomm_create ( MPI_Comm local_comm, int local_leader,
MPI_Comm peer_comm, int remote_leader, int tag,
MPI_Comm *comm_out )

local_comm->workers_comm
local_leader->0 (not know exactly what means. Is this the starting value of the ranking in local_comm)
peer_comm-> Is this for my example MPI_COMM_WORLD (the excluding rank 0 has still this comm?)
remote leader->(same question as local)
tag-> whatever
comm_out-> new communicator

Code:

#include "mpi.h" 
#include <stdio.h>
int main(argc,argv) 
int argc; 
char *argv[]; { 
  int rank,rank2,group_size,group_size2,comm_size,comm_size2,new_rank, sendbuf, recvbuf, server=0;
  int ranks[1],workersid, workersize;
  int array2, array1,array3;
  int color=4,mpi_errno;

 MPI_Comm world,workers_comm,workers,cowork_comm; 
 MPI_Group worker_group, world_group;

 MPI_Init(&argc,&argv); 
 MPI_Comm_rank(MPI_COMM_WORLD, &rank);
 MPI_Comm_size(MPI_COMM_WORLD, &comm_size);
MPI_Status status;
 ranks[0]=server;

 printf("rank= %d comm_size=%d \n",rank, comm_size);

 world=MPI_COMM_WORLD;

 MPI_Comm_group(world,&world_group);

 MPI_Group_excl(world_group,1,ranks,&worker_group);

 MPI_Comm_create(world,worker_group,&workers);


 if(rank!=0){
 MPI_Comm_rank(workers,&workersid); 
 MPI_Comm_size(workers,&workersize);
 
 printf("workersid= %d workersize=%d \n",workersid,workersize);
  array1=workersid;

 if ((workersid>0) && (workersid<4)){color=1;}
 if ((workersid>3)&& (workersid<7)){color=2;}
 if ((workersid>6)&& (workersid<10)){color=3;}
 if ((workersid>9)&& (workersid<21)){color=4;}


 MPI_Comm_split(workers,color,workersid,&workers_comm);


 MPI_Comm_rank(workers_comm,&rank2);
 MPI_Comm_size(workers_comm,&comm_size2);


 printf("size=%d  size2= %d comm_size2=%d new rank= %d\n",group_size,group_size2, comm_size2,rank2);
 
 
  MPI_Allreduce(&array1,&array2,1,MPI_INT,MPI_SUM,workers_comm);

  printf("array1=%d  array2= %d comm_size2=%d new rank= %d\n",array1,array2, comm_size2,rank2);
 

 /*MPI_Barrier(workers_comm);*/
 

  MPI_Intercomm_create(workers_comm,0,world,0,99,&cowork_comm);


   printf("\n........\n");
 
  /*MPI_Send(&array2,0,MPI_INT,0,9,cowork_comm);*/
 }
  */
 

 if(rank==0){
/*MPI_Recv(&array,1,MPI_INT,0,9,cowork_comm, &status)*/
printf("array1 = %d array2= %d\n",array1,array2);
 }
 if (rank!=0){ 
 MPI_Comm_free(&workers_comm); 
 MPI_Comm_free(&cowork_comm);
 
 MPI_Comm_free(&workers);
 MPI_Group_free(&worker_group);
 }

 MPI_Finalize();
}

The execution holds on MPI_Intercomm
mpirun -n 10 ...

with mpich1

Code:

rank= 1 comm_size=10 
rank= 2 comm_size=10 
rank= 3 comm_size=10 
rank= 4 comm_size=10 
rank= 5 comm_size=10 
rank= 6 comm_size=10 
rank= 7 comm_size=10 
rank= 8 comm_size=10 
rank= 0 comm_size=10 
rank= 9 comm_size=10 
workersid= 2 workersize=9 
workersid= 5 workersize=9 
workersid= 7 workersize=9 
array1 = 0 array2= 0
workersid= 0 workersize=9 
workersid= 4 workersize=9 
workersid= 6 workersize=9 
workersid= 3 workersize=9 
workersid= 8 workersize=9 
workersid= 1 workersize=9 
size=32681  size2= 4417456 comm_size2=3 new rank= 0
size=32681  size2= 4417456 comm_size2=3 new rank= 2
size=32681  size2= 4417456 comm_size2=2 new rank= 0
size=32681  size2= 4417456 comm_size2=3 new rank= 1
size=32681  size2= 4417456 comm_size2=3 new rank= 1
size=32681  size2= 4417456 comm_size2=1 new rank= 0
size=32681  size2= 4417456 comm_size2=3 new rank= 0
array1=0  array2= 0 comm_size2=1 new rank= 0
array1=2  array2= 6 comm_size2=3 new rank= 1
size=32681  size2= 4417456 comm_size2=2 new rank= 1
array1=3  array2= 6 comm_size2=3 new rank= 2
array1=8  array2= 15 comm_size2=2 new rank= 1
array1=7  array2= 15 comm_size2=2 new rank= 0
array1=1  array2= 6 comm_size2=3 new rank= 0
size=32681  size2= 4417456 comm_size2=3 new rank= 2
array1=6  array2= 15 comm_size2=3 new rank= 2
array1=5  array2= 15 comm_size2=3 new rank= 1
array1=4  array2= 15 comm_size2=3 new rank= 0

any help welcome

the */ after the

/*MPI_Send(&array2,0,MPI_INT,0,9,cowork_comm);*/
}

shouldnt be there but it's a typo; it's not the problem