Intercommunicators in MPI-1

• Communication between two disjoint groups
  
• In many functions the communicator argument can be an intercommuncator
  exception (in MPI-1): collective operations
• Rank of a task:
  • relative to own group for local operation
  • relative to other group for remote operation
• Example: send and receive with intercommunicator
  

  • intercommunicator between group A and group B
  • task 1 of group A sends to task 2 of group B
  • task 1 of A: MPI_Send(..., 2, ... intercomm)
  • task 2 of B: MPI_Recv(..., 1, ... intercomm,...)
• Creation of an intracommunicator with
  MPI_Intercomm_create(MPI_Comm local_comm, int local_leader, MPI_Comm peer_comm, int remote_leader, int tag, MPI_Comm *newintercomm)
  quite complicated
  functions for dynamic process creation return an intercommunicator
• Merging of an intercommunicator to an intracommunicator containing both groups:
  MPI_Intercomm_merge(MPI_Comm inter, int high, MPI_Comm *intra)