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random.gammavariate

distributions

A random number from the gamma distribution (alpha>0, beta>0); always positive.

Syntax

random.gammavariate(alpha, beta)

Here beta is the scale, so the mean is alpha*beta — that is why alpha=2, beta=3 averages around 6. Many textbooks and libraries define beta the other way round, as a rate, so a formula copied from elsewhere often has to be converted to 1/beta. This has nothing to do with the mathematical gamma function (math.gamma), and both alpha and beta must be strictly positive or you get a ValueError.

Examples

import random
print(random.gammavariate(2.0, 3.0) > 0.0)   # → True
print(type(random.gammavariate(2.0, 3.0)).__name__)   # → float
print(round(sum(random.gammavariate(2.0, 3.0) for _ in range(10000)) / 10000))   # → 6
print(random.gammavariate(1.0, 2.0) > 0.0)   # → True
print(random.gammavariate(0.0, 3.0))   # → ValueError

See also

Common errors

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