function [sys,x0,str,ts]=MIMO_Tong_plant(t,x,u,flag)
switch flag,
case 0,
    [sys,x0,str,ts]=mdlInitializeSizes;
case 1,
    sys=mdlDerivatives(t,x,u);
case 3,
    sys=mdlOutputs(t,x,u);
case {2, 4, 9 }
    sys = [];
otherwise
    error(['Unhandled flag = ',num2str(flag)]);
end
function [sys,x0,str,ts]=mdlInitializeSizes
sizes = simsizes;
sizes.NumContStates  = 4;
sizes.NumDiscStates  = 0;
sizes.NumOutputs     = 6;
sizes.NumInputs      = 4;
sizes.DirFeedthrough = 0;
sizes.NumSampleTimes = 0;
sys=simsizes(sizes);
x0=[0 0 0 0];
str=[];
ts=[];
function sys=mdlDerivatives(t,x,u)   %Ref to PID411
r1=1;r2=0.8;
m1=1;m2=1.5;

D11=(m1+m2)*r1^2+m2*r2^2+2*m2*r1*r2*cos(x(3));
D22=m2*r2^2;
D21=m2*r2^2+m2*r1*r2*cos(x(3));
D12=D21;
D=[D11 D12;D21 D22];

C12=m2*r1*sin(x(3));
C=[-C12*x(4) -C12*(x(2)+x(4));C12*x(1) 0];

g1=(m1+m2)*r1*cos(x(3))+m2*r2*cos(x(1)+x(3));
g2=m2*r2*cos(x(1)+x(3));
G=[g1;g2];

Fr=[3*x(2)+0.2*sign(x(2));2*x(4)+0.2*sign(x(4))];
told=[0.05*sin(20*t);0.1*sin(20*t)];
F=told+Fr;

tol=[u(1) u(2)]';
S=inv(D)*(tol-C*[x(2);x(4)]-G-F);

sys(1)=x(2);
sys(2)=S(1);
sys(3)=x(4);
sys(4)=S(2);
function sys=mdlOutputs(t,x,u)
Fr=[3*x(2)+0.2*sign(x(2));2*x(4)+0.2*sign(x(4))];
told=[0.05*sin(20*t);0.1*sin(20*t)];
F=told+Fr;

sys(1)=x(1);
sys(2)=x(2);
sys(3)=x(3);
sys(4)=x(4);
sys(5)=F(1);
sys(6)=F(2);