Although some of them are actually not constant, their behaviours are easy to guess. Fig. 5 shows the effect of c on ∂f1/∂p1, ∂f1/∂p2 and ∂f1/∂p3. While a12=∂f1/∂p1 is constant, a12=∂f1/∂p2 and a13=∂f1/∂p3 are completely proportional to c. Therefore, it would be easy to modify a12 and a13 after once calculating c using Eq. (8) as follows: