human
I wrote the below code

    a = (1.0 + abruptness)
    def _f(t):
        f1 = (lambda t: ((0.5 ** (1 - a)) * (t ** a)))
        f2 = (lambda t: (1 - f1((1 - t))))
        return (((t < 0.5) * f1(t)) + ((t >= 0.5) * f2(t)))
    return (old_d * _f(((t / new_d) ** soonness)))

What's a good function header?
assistant
#Here's a good function header.

def f_accel_decel(t, old_d, new_d, abruptness=1, soonness=1.0):