https://en.wikipedia.org/wiki/Beta_function#Incomplete_beta_function
This function looks at the values of x, a, and b, and determines which algorithm is best to calculate
the value of Iₓ(a, b)
http://www.boost.org/doc/libs/1_35_0/libs/math/doc/sf_and_dist/html/math_toolkit/special/sf_beta/ibeta_function.html
https://github.com/boostorg/math/blob/develop/include/boost/math/special_functions/beta.hpp
public static regularizedIncompleteBeta ( $x, $a, $b ) : number | ||
$x | Upper limit of the integration 0 ≦ x ≦ 1 | |
$a | Shape parameter a > 0 | |
$b | Shape parameter b > 0 | |
return | number |