Vel factory function

def create(entropy_coefficient, value_coefficient, cliprange, max_grad_norm, discount_factor,
           normalize_advantage=True, gae_lambda=1.0):
    """ Vel factory function """
    return PpoPolicyGradient(
        entropy_coefficient, value_coefficient, cliprange, max_grad_norm,
        discount_factor=discount_factor,
        normalize_advantage=normalize_advantage,
        gae_lambda=gae_lambda
    )