BETAI Function
Evaluates the real incomplete beta function Ix = βx (y, z)/β(y, z).
Usage
result = BETAI(x, y, z)
Input Parameters
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.
Returned Value
result—The value of the incomplete beta function.
Input Keywords
Double—If present and nonzero, double precision is used.
Discussion
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.
Example
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
