Erlang Distribution

The Erlang distribution is the time to complete a fixed number of identical exponential stages one after another. It is a gamma distribution whose shape is a whole number, and it is common in service and queueing models.

Write Erlang(stages, rate), where stages is a positive whole number:

Erlang(3, 0.5)

adds up three exponential stages. Use it for a task made of several equal sub-steps, which gives a more realistic, less variable time than a single exponential.