# Cumulative distribution function¶

btdtr(a, b, x)
Returns the area from zero to x under the beta density function.
Parameters: a (float) – a positive number b (float) – a positive number x (float) – any number within [0, 1]

See also incbet().

## Description¶

Returns the area from zero to x under the beta density function:

$P(x~|~a, b) = \frac{\Gamma(a+b)}{\Gamma(a)+\Gamma(b)} \int_0^xt^{a-1}(1-t)^{b-1} dt$

This function is identical to the incomplete beta integral function incbet().

The complemented function is:

1 - P(1-x | a, b) = incbet( b, a, x )