MATLAB: Multi-input state space solution using ODE45

Question

I have the linear dynamics set up as follows:

function dx = sys(t,x)
    global c m g r J 
    A = [0 0  0  1   0  0
         0 0  0  0   1  0
         0 0  0  0   0  1
         0 0 -g -c/m 0  0
         0 0  0  0 -c/m 0
         0 0  0  0   0  0];
    B = [0    0
         0    0 
         0    0
         1/m  0
         0   1/m
         r/J  0];
    K = [-3.1623 0.0000 20.1673 -4.7754 0.0000 4.4257
          0.0000 3.1623  0.0000  0.0000 5.8914 0.0000];
    u = K*x;
    dx = A*x + B*u;
    end

And the call to the solution:

global c m g r J 
m = 4;        
J = 0.0475;   
r = 0.055;    
g = 9.8;      
c = 0.05;     
tspan = [0 10];                            
iniCon = [-1; -1; 0; 0; 0; 0; 0; 0];               
[t,y] = ode45(@(t,x) sys(t,x),tspan,iniCon);  
plot(t,y)

When I run the solution I get an error saying that the inner dimensions of u = K*x do not match. Does anyone know where the mistake is?

Thanks

Answer 1

K is (2x6) and x is (8x1), thus K*x is not defined.

Best wishes

Torsten.