python (SimPy) generate random numbers that follow the erlang distribution

Question

I am using Python (SimPy package mostly, but it is irrelevant to the question I think), modeling some systems and running simulations. For this purpose I need to produce random numbers that follow distributions. I have done alright so far with some distributions like exponential and normal by importing the random (eg from random import *) and using the expovariate or normalvariate methods. However I cannot find any method in random that produce numbers that follow the Erlang distribution. So:

1. Is there some method that I overlooked?
2. Do I have to import some other library?
3. Can I make some workaround? (In think that I can use the Exponential distribution to produce random “Erlang” numbers but I am not sure how. A piece of code might help me.

Thank you in advance!

Answer 1

Erlang distribution is a special case of the gamma distribution, which exists as numpy.random.gamma (reference). Just use an integer value for the k ("shape") argument. See also about scipy.stats.gamma for functions with the PDF, CDF etc.

Answer 2

As the previous answer stated, the erlang distribution is a special case of the gamma distribution. As far as I know, you do not, however, need the numpy package. Random numbers from a gamma distribution can be generated in python using random.gammavariate(alpha, beta).

Usage:

import random
print random.gammavariate(3,1)