reports the amount of wall clock time for det_by_minor
to compute the determinant of a square matrix.
It specifies the number of rows (and columns) in the square matrix
that the determinant is being calculated for.
It specifies the minimum amount of time in seconds
routine should take.
The calculations is repeated the necessary number of times so that
this amount of execution time (or more) is reached.
The return value
and is the number of wall clock seconds that it took for
det_by_minor to compute its determinant
(plus overhead which includes choosing a random matrix).