Asked by Eloy Pena Asensio
on 20 Aug 2018

Hello everybody.

I am trying to implement an adaptive filter identification system. The mass is variable so I have to calculate with Matlab (no Simulink) each transfer function for each mass. The problem is the continuity: I have all the state spaces but I can not solve de last "position" in order to introduce it as initial condition in the next state space.

I have state space equation like:

xdot=A.x+B.u(t) where u=sen(t)

y= C.x where C is [0 C2] so I can solve x2 because I know the value of the amplitude y(t).

The problem is that I can not solve x1, I dont know how to use ode45 for this.

The purpose is to use lsim(sys,u,t,x0) where x0=[x1 x2]

How could I resolve the value of x1 in the last position of my last state space?

A =

x1 x2

x1 -4 -12.5

x2 8 0

B =

u1

x1 4

x2 0

C =

x1 x2

y1 0 3.125

D =

u1

y1 0

As aspicted in the attached figure, the next state space starts in the correct position (last state space position) because I solved x2 but not with the proper velocity and acceleration because I didnt solve x1. The mass changes in each vertical line, the mass change point is marked with a circle

Answer by Akshay Khadse
on 29 Aug 2018

For using “ode45”, you will need to create a MATLAB function independent of “u” by substituting “sin(t)” in its place. Then, the “ode45” could be used as

[t,x] = ode45(@functionName,tspan,y0);

where “tspan = [t0 tf]” is the vector with start and end time of the solution and “y0” is the initial condition vector

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