Replace the MPI_Send and MPI_Recv calls in your solution with two calls to
MPI_Sendrecv. The first call should shift data up; that is, it should send
data to the processor above and receive data from the processor below. The
second call to MPI_Sendrecv should reverse this; it should send data to the
processor below and receive from the processor above.
You may want to use these MPI routines in your solution:
MPI_Sendrecv