$3\mathrm{.}7$ A ping$-$pong is a communication in which two messages are sent, first from

process A to process B $($ping$),$ and then from process B back to process A

$($pong$).$ Timing blocks of repeated ping$-$pongs is a common way to estimate

the cost of sending messages. Time a ping$-$pong program using the C clock

function on your system. How long does the code have to run before clock

gives a nonzero run$-$time? How do the times you got with the clock function

compare to times taken with MPI$\_$Wtime