# 3.5.1.3.40 IncBeta

## Description

This function is used to calculate the incomplete Beta function with parameters x, a, and b, which is denoted by: $incbeta(x,a,b)=\frac{1}{B(a,b)}\int_{0}^{x} t^{a-1}(1-t)^{b-1}dt$

where B(a,b) is the Beta function.

## Syntax

double incbeta(double x, double a, double b)

## Parameters

x

Input parameter. The value of the x variate, must lie on the interval [0, 1].

a

Input parameter. The first shape parameter, a, of the required beta distribution, must be positive( a>0 ).

b

Input parameter. The second shape parameter, b, of the required beta distribution, must be positive ( b>0 ).

## Return

Returns the value of Beta function with parameters x, a and b.

## Example

aa = incbeta(1,2,2);
aa = ; //should return 1