Comparing: Collective communications

Collective communication in MPI

To perform collective communication on a subset of processes a new communicator has to be created.

Distribution of data amongst processes in MPI

• MPI_BCAST

• MPI_SCATTER

• MPI_GATHER

• MPI_ALLGATHER

MPI reduction operators

• Global Reduction Operators.
  These are used to compute a result that involves data distributed across a group of processes.
• Reduction operators may be pre-defined or user-defined.
• Predefined operators include:

  	MPI_MAX 	Maximum
  	MPI_MIN 	Minimum
  	MPI_SUM 	Sum
  	MPI_PROD	Product
  	MPI_IAND	Logical AND
  	MPI_BAND	Bitwise AND
  

Collective Communication in PVM

• Any PVM task can join or leave a group without having to inform other tasks.

Joining and leaving groups in PVM

• pvmfjoingroup(group,inum)

  Where:

  group

  is a character string of an existing group

  inum

  is the instance number of this task joining the group

• pvmflvgroup(group,info)

  Where:

  info

  is an integer status code

Broadcasting messages in PVM

pvmfbcast(group, msgtag, info)