Particle Effective Sample Size

Problem

Compute the effective sample size of a normalized weight vector: ESS = 1 / sum(w_i^2).

Return 0.0 when the list is empty or all weights are zero. Uniform weights over n particles give exactly n.

Hint

Concentrated weights drive the sum of squares up and the effective size down.

case 1

in: [[0.5,0.5]]

expected: 2

case 2

in: [[1]]

expected: 1

case 3

in: [[0.25,0.25,0.25,0.25]]

expected: 4

case 4

in: [[]]

expected: 0

case 5

in: [[0.1,0.2,0.7]]

expected: 1.851851851851852

Starter codePython

def particle_effective_sample_size(weights):
    # Your code here
    pass

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