Internal function for going back to the original scale.
a vector or matrix with values normalized between -1 and 1, this vector was obtained when normalizing a vector or matrix x.
If z is a vector, base is the minimum of x. If x is a matrix, base is a vector with the minimum for each of the columns of the matrix x.
if z is a vector, spread=base-max(x). If x is a matrix, spread is a vector calculated for each of the columns of x.
A vector or matrix with the resulting un normalized values.