This example shows how performance can be harmed by specifying excessive synchronization. Form a grid of processors containing 4 rows and 3 columns. Have each processor send len (default of 2048) MPI_DOUBLE to the 4 neighboring processors in the order down, right, up, left. The grid of processors is NOT periodic. That is, the processors on the bottom row do not send down, the processors in the rightmost column do not send right, etc. Use MPI_Irecv to post receives for each of the four directions. Use MPI_Send to send in the order down, right, up, left. Observe the time that each MPI_Send takes.