BETAI Function

Evaluates the real incomplete beta function I_x = b_x (y, z)/b(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 I_0.61 = b_0.61 (2.2,3.7)/b(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