def _build_func(eq, **args):
    """
    Take a symbolic equation and return the lambdified version plus the
    linearization of form S1 * x + S2
    """
    from sympy import lambdify
    eq_prime = eq.diff(args['x'])
    s1 = eq_prime
    s2 = eq - eq_prime * args['x']
    EQ = lambdify(args.values(), expr=eq, modules='numpy')
    S1 = lambdify(args.values(), expr=s1, modules='numpy')
    S2 = lambdify(args.values(), expr=s2, modules='numpy')
    return EQ, S1, S2
