Hi, I have a 'simplified' equation of the magnetically suspended ball. a = g - (i/h * M) where a - actual acceleration of the ball. h - distance from the magnet. g - gravitational acceleration, to keep it simple let g = 10 M - mass of the ball 0.05 kg i - current through the coil = how strong the magnet is. I need to make a simulation where controller's input 'u' is distance of the ball from magnet and 'y' from the controller is current 'i' of the magnet. The output y directly puts current into the coil (its just processing simulation with a falling ball). To keep it simple, no observer is required. My suggested solution: state x consists of [x1, x2, x3] = [h, v, i] h - dist. from magnet v - velocity of the ball i - current so steady state x0 = [10,0,5] But I do not know how to make matrixes A and B to build model: x_dot = Ax + Bu I started to compute matrix A as a Jacobian matrix but can not compute 3rd raw of the matrix. Maybe jacobian is not necessary. could anybody help me please? Thx.