Another interesting question is the following: since the size and shape of the tiles may be imposed by some a priori considerations (such as the cache size,
and the results on the best communication-to-computation ratio that have been reviewed in Section 2.1), we may consider 
and 
as input parameters
and try to determine what is the optimal number of processors that should be used so as
to minimize the total execution time.
The answer is given by the following proposition:
