Focal Loss Gamma Reduction

Problem

Compute how much focal loss reduces the mean cross-entropy. Use mean CE minus mean focal loss with focusing parameter gamma and alpha 1, where p_t is p for y = 1 and 1 - p otherwise, with probabilities clipped to [1e-15, 1 - 1e-15]. Return 0.0 for empty input.

Hint

A larger gamma focuses more of the loss on hard, misclassified examples.

Test cases

case 1

in: [[1,0],[0.9,0.9],2]

expected: 0.2708990390850584

case 2

in: [[1,1],[0.6,0.6],0]

expected: 0

case 3

in: [[0,1],[0.3,0.3],1]

expected: 0.3054321510274468

case 4

in: [[],[],2]

expected: 0

Starter codePython

import math

def focal_gamma_reduction(y_true, probs, gamma):
    # Your code here
    pass

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