returns pseudo-random values drawn from a uniform distribution with lower
and upper limits LOWER and UPPER.
LOWER and UPPER can also be matrices of the same shape as rand(N) would
N is a vector indicating the dimensions of the output:
N =  creates a 3x3 matrix
N = [1,3] creates a 1x3 matrix
N = [17,1,3] creates a 17x1x3 matrix
LOWER and UPPER can be any number