Beta Distribution Mean and Variance

Problem

For a Beta(alpha, beta) distribution, return [mean, variance]. mean = alpha / (alpha + beta) and variance = alpha * beta / ((alpha + beta)^2 * (alpha + beta + 1)). Return [0.0, 0.0] when either parameter is nonpositive.

Hint

Divide the normalization constants; the sum alpha + beta controls the spread.

Test cases

case 1

in: [1,1]

expected: [0.5,0.08333333333333333]

case 2

in: [2,3]

expected: [0.4,0.04]

case 3

in: [0.5,0.5]

expected: [0.5,0.125]

case 4

in: [2,2]

expected: [0.5,0.05]

case 5

in: [0,1]

expected: [0,0]

Starter codePython

def beta_mean_variance(alpha, beta):
    # Your code here
    pass

5 test cases · run your code against them in the editor