Returns the cumulative beta probability density function. The cumulative beta probability density function is commonly used to study variation in the percentage of something across samples, such as the fraction of the day people spend watching television.

Parameters :

	X	is the value between A and B at which to evaluate the function.
	Alpha	is a parameter of the distribution.
	Beta	is a parameter of the distribution.
	A	is an optional lower bound to the interval of x. (=0)
	B	is an optional upper bound to the interval of x.(=1)