Hyper-Erlang distribution

In probability theory, a hyper-Erlang distribution is a continuous probability distribution which takes a particular Erlang distribution Ei with probability pi. A hyper-Erlang distributed random variable X has a probability density function given by A ( x ) = ∑ i = 1 n p i E l i ( x ) {\displaystyle A(x)=\sum _{i=1}^{n}p_{i}E_{l_{i}}(x)} where each pi > 0 with the pi summing to 1 and each of the Eli being an Erlang distribution with li stages each of which has parameter λi.

Source: Wikipedia — Hyper-Erlang distribution (CC BY-SA 4.0)