Evaluates the real incomplete beta function Ix = βx (y, z)/β(y, z).

x—Point at which the incomplete beta function is to be evaluated.

y—Point at which the incomplete beta function is to be evaluated.

z—Point at which the incomplete beta function is to be evaluated.

result—The value of the incomplete beta function.

Double—If present and nonzero, double precision is used.

The incomplete beta function is defined to be:

The incomplete beta function requires that 0 ≤ x ≤ 1, y > 0, and z > 0. It underflows for sufficiently small x and large y. This underflow is not reported as an error. Instead, the value zero is returned.

Evaluate the log of the incomplete beta function I0.61 = β0.61 (2.2,3.7)/β(2.2,3.7).

x  =  0.61

y  =  2.2

z  =  3.7

ans  =  BETAI(x, y, z)

PRINT, 'beta incomplete =', ans  ; beta incomplete = 0.882172