How to plot each state space variables seperatly

I created a state space system and I want to analyze the step response of each state space variable (x1, x2, x3...) seperatly. I'm not quite sure How am I suppose to access them. I've used the step command to creat vectors x and y, but I don't know how to creat a figure of x(t) (again, x1, x2, x3), and when Itry to access X or Y MATLAB tells me that the arrays are emptey, i would really like some help becasue I'm pretty new at MATLAB.

Thanks in advance!

My code so far:

A = [-1 4 0; 0 3 0; 0 0 -2];
B = [1 1 1];
B = transpose(B);
C = [-1 1 2];
sys = ss(A,[],C,[], 'StateName', {'x1' 'x2' 'x3'});
t = (0:0.1:5)';
[y, t, x] = step(sys,t);
plot(t, x(1));

Answer 1

[David Wilson]

Couple of things. First up, you haven't inserted B into your state-space model so consequently you don't get any output.

To get the individual states, just access the relevant column of the outputted x variable.

A = [-1 4 0; 0 3 0; 0 0 -2]; % note unstable, check eig(A) 
B = [1 1 1]';  % note transpose
C = [-1 1 2];
sys = ss(A,B,C,[], 'StateName', {'x1' 'x2' 'x3'});  % note B is used ! 
t = [0:0.1:5]';
[y, t, x] = step(sys,t);

for i=1:3
  subplot(3,1,i); 
  plot(t, x(:,i));  % look at how I indexed into x 
end 

[Ritvik Srivant]

Thanks this literally saved me from grave. lol :)