What IS MPI

一、MPI message passing interface

A specification for the developers and users of message passing libraries.

By itself, it is an interface not a library.

Commonly used for distributed memory system & high-performance computing

Goal:

Portable: Run on different machines or platforms

Scalable:Run on million of compute nodes

Flexible:isolate MPI developers from MPI programme(users)

Programming Model

SPMD:Single Program Multiple Data

Allow tasks to branch or conditionally execute only parts of the program they are designed to execute

MPI tasks of a parallel program can not be dynamatically spawned during run time.

Distributed memory

MPI provide method of sending &receiving message

二、Communication Methods

From the view of the pair of communicated processes

From the view of individual function call

Communicators and Groups

Groups define which collection of processes may communicate with each other

Each group is associated with a communicator to perform its communication function calls

MPI_COMM_WORLD is the pre-defined communicator for all processors

MPI_INIT():

• Initializes the MPI execution environment
• Must be called before any other MPI functions
• Must be called only once in an MPI program

MPI_FINALIZE():

• Terminates the MPI execution environment
• No other MPI routines may be called after it