Polyak Step Size

Problem

Compute the Polyak step size.

Return (f_current - f_best) / grad_norm_sq, or 0.0 if grad_norm_sq is not positive. This assumes the optimal objective value f_best is known.

Hint

The step shrinks as the current gap to the optimum shrinks.

case 1

in: [10,5,4]

expected: 1.25

case 2

in: [1,1,2]

expected: 0

case 3

in: [3,0,0]

expected: 0

case 4

in: [2.5,1,6]

expected: 0.25

Starter codePython

def polyak_step_size(f_current, f_best, grad_norm_sq):
    # Your code here
    pass

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