I Sending and Receiving Messages Sending messages is straightforward. The source( the identity of the sender) is determined implicitly, but the rest of the message (envelope and body) is given explicitly by the sending process Receiving messages is not quite so simple. As a process may have several pending messages To receive a message, a process specifies a message envelope that MPI compares to the envelopes of pending messages. If there is a match, a message is received otherwise, the receive operation cannot be completed until a matching message is sent In addition, the process receiving a message must provide storage into which the body of the message can be copied. The receiving process must be careful to provide enough storage for the entire messageSending and Receiving Messages • Sending messages is straightforward. The source (the identity of the sender) is determined implicitly, but the rest of the message (envelope and body) is given explicitly by the sending process. • Receiving messages is not quite so simple. As a process may have several pending messages. • To receive a message, a process specifies a message envelope that MPI compares to the envelopes of pending messages. If there is a match, a message is received. Otherwise, the receive operation cannot be completed until a matching message is sent. • In addition, the process receiving a message must provide storage into which the body of the message can be copied. The receiving process must be careful to provide enough storage for the entire message