c - comm_split strange behavior? -

i have spent quite few hours trying figure out have come here help. learning mpi , problem since new don't know why weird behavior occurs. trying have 8 numbers spread across 8 processors follows. split communicator exchange elements sub communicator follows:

0 1 2 3 4 5 6 7

split

0 1 2 3 | 4 5 6 7

exchange

2 3 0 1 | 6 7 4 5

the output 4 5 6 7 0 1 2 3 output should 2 3 0 1 6 7 4 5. can on why giving me strange result?

#include <stdio.h> #include <stdlib.h> #include <mpi.h> #include <math.h> int main(argc,argv) int argc; char *argv[];  {     int myid, numprocs;     int color,zero_one,new_id,new_nodes;     mpi_comm new_comm;      mpi_init(&argc,&argv);     mpi_comm_size(mpi_comm_world,&numprocs);     mpi_comm_rank(mpi_comm_world,&myid);       int my_num, my_received;         int old_id;       switch(myid){          case 0:             my_num = 0;             old_id = 0;          break;           case 1:             my_num = 1;             old_id = 1;          break;          case 2:             my_num = 2;             old_id = 2;          break;          case 3:             my_num = 3;             old_id = 3;          break;          case 4:             my_num = 4;             old_id = 4;          break;          case 5:             my_num = 5;             old_id = 5;          break;          case 6:             my_num = 6;             old_id = 6;          break;          case 7:             my_num = 7;             old_id = 7;          break;       }  //here split      color=myid % 2;     mpi_comm_split(mpi_comm_world,color,myid,&new_comm);     mpi_comm_rank( new_comm, &new_id);     mpi_comm_rank( new_comm, &new_nodes);      //here exchange in sub list or communicator          if(new_id < 2){              mpi_send(&my_num, 1, mpi_int,  2 + new_id, 0, new_comm);             mpi_recv(&my_received, 1, mpi_int, 2 + new_id, 0, new_comm, mpi_status_ignore);                   }         else         {             mpi_recv(&my_received, 1, mpi_int, new_id - 2, 0, new_comm, mpi_status_ignore);                      mpi_send(&my_num, 1, mpi_int, new_id - 2 , 0, new_comm);           }        printf("old_id= %d received num= %d\n", old_id, my_received);       mpi_finalize();  } 

running program get:

old_id= 4 received num= 0 old_id= 5 received num= 1 old_id= 1 received num= 5 old_id= 3 received num= 7 old_id= 6 received num= 2 old_id= 7 received num= 3 old_id= 0 received num= 4 old_id= 2 received num= 6 

according split, ranks collected in 1 communicator , odds in another:

old_id= 0 received num= 4 old_id= 2 received num= 6 old_id= 4 received num= 0 old_id= 6 received num= 2 

and:

old_id= 1 received num= 5 old_id= 3 received num= 7 old_id= 5 received num= 1 old_id= 7 received num= 3 

which looks thing asked for. either can't reproduce problem, misunderstood or nothing wrong?