How to plot the step response of a state space representation using ODE45

I need to plot the step response of a system with a spring as a link.

The two derived differential equations are :

• m1(x1'') = U - k(x1-x2)
• m2(x2'') = k(x1-x2)

The state space representation is:

• A = [0 1 0 0; -k/m1 0 k/m1 0; 0 0 0 1; k/m2 0 -k/m2 0];
• B = [0; 1/m1 ;0 ;0];
• C = [1 0 -1 0];
• D = 0;

I can not use the step(A,B,C,D) function and it must be solved with ode45, how is that done?

Answer 1

[bio lim]

Define your closed loop system in your function definition. Then set your input as U = 1, and use ode45 to get the response.