As discussed in Section 4.6, MPI offers a number of variants of send including the MPI_Rsend
operation, which assumes the receiver is ready to receive at the time of sending. What
optimizations in implementation are possible if this assumption is correct and what are the
repercussions of this assumption being false?

What will be an ideal response?

The key optimization is that the sender does not have to check that the receiver is ready to receive a message
and this therefore avoids a handshake between sender and receiver, increasing the performance of the
implementation. If the receiver is not ready, the outcome of the send operation is unpredictable in terms of the
buffer being ready and the MPI documentation deems the outcome undefined. It may be for example that
values will be over-written before being consumed.