Hi, I want to calculate "a" in the following equation using the Newton- Raphson method: With M, phi1 nad phi2 are matrices and S is given by: Besically all the variables are known apart from "a" thus using newton raphson we can find "a". The way I have approached his is by taking the derivative of S wit hrespect to "a", thus In matlab, I enter all these equations and state that for Newton Raphson: I then loop this a couple of times. Every loop generates a new "a" which is entered and the equations calculated again and again derived. But you guessed, it is not working. Now, I was hoping someone could tell me if I had made errors towards the derivation during the various steps or not. Or maybe someone spots an other problem?