def get_ancestral_step(sigma_from, sigma_to):
    """Calculates the noise level (sigma_down) to step down to and the amount
    of noise to add (sigma_up) when doing an ancestral sampling step."""
    sigma_up = (sigma_to**2 * (sigma_from**2 - sigma_to**2) / sigma_from**2) ** 0.5
    sigma_down = (sigma_to**2 - sigma_up**2) ** 0.5
    return sigma_down, sigma_up
Calculates the noise level (sigma_down) to step down to and the amount
of noise to add (sigma_up) when doing an ancestral sampling step.
modules/diffusion/karras/karras_diffusion.py