Stretched Beta Law

Parameters $$-\infty < min < mode < max < +\infty $$
Support $$x \in \mathbb{R} \quad and \quad p \in \:]0,1 [$$
PDF $$ PDF = \frac{x^{(a-1)} (1-x)^{(b-1)}}{ B(a,b)} $$
$$ with \qquad B(a,b)= \frac{\Gamma(a)+ \Gamma(b)}{ \Gamma(a+b)} , \qquad the \, Beta \, function $$
$$ with \qquad \Gamma(.)= Gamma \, function $$
$$ with \qquad \left\{ \begin{array}{rl}
a = 1+4 \left( \frac{mode-min}{(max-min)} \right),\\
b = 1+4 \left( \frac{max-mode}{(max-min)} \right),
\end{array} \right. \qquad
according \, to \, PERT \, method $$
CDF $$ CDF = I_{x}(a,b)$$
$$ with \qquad I_{x}(a,b)= \frac{B(x;a,b)}{ B(a,b)} , \qquad the \, Incomplete \, beta \, function $$
$$ with \qquad \left\{ \begin{array}{rl}
a = 1+4 \left( \frac{mode-min}{(max-min)} \right),\\
b = 1+4 \left( \frac{max-mode}{(max-min)} \right),
\end{array} \right. \qquad
according \, to \, PERT \, method $$
CDF-1 $$ CDF^{-1} = I^{-1}_{x}(a,b)$$
$$ with \qquad I^{-1}_{p}(a,b) , \qquad the \, Inverse \, incomplete \, beta \, function $$