Normal random numbers
X = rnorm( [ n,m,s])
positive integer or a 2-vector [lig, col] of positive integers. this argument is optional its default value is 1.
mean, optional scalar with default value 0
standard deviation, optional scalar with default value 1
n-vector or n-matrix of normal random numbers with mean m and standard deviation s.
Returns random deviates from the normal distribution with mean m and standard deviation s.