def polynomial_3_differential(x, a, b, c, d):
    """Polynomial order 3 where f(x) = a + b * x + c * x**2 + d * x**3
    Differential(f(x) = b + 2.0 * c * x**1 + 3.0 * d * x**2
    """
    return b + 2.0 * c * x + 3.0 * d * x**2