Generate Sample from Beta distribution

For Generate Random Sample, the Beta distribution can be defined by its Mean and Variance or by two shape parameters a and b. The mean is equal to a(a+b)⁻¹ with variance ab(a+b+1)⁻¹(a+b)⁻²;. By default, the two-parameter form is used, defined on the range (0,1). By setting the lower and upper bounds the four-parameter form can be used, defined on the specified range and the mean between them must be within the specified range.