the first argument of B, must be positive
the second argument of B, must be positive
the fraction of integration completion from below, 0 $(LE) x $(LE) 1
It returns Ix(a,b), an element of [0,1].
Note: The integral is evaluated by a continued fraction expansion or, when b * x is small, by a power series.
Regularized incomplete beta function Ix(a,b)
Mathematically, if a and b are positive real numbers, and 0 $(LE) x $(LE) 1, then Ix(a,b) = $(INTEGRATE 0, x)ta-1(1-t)b-1dt/B(a,b) where B is the beta function. It is also the cumulative distribution function of the beta distribution.
betaIncomplete(a, b, x) evaluates Ix(a,b).