function dx=c3ex1(t,x)
  u=2*cos(x(1)+pi/6)-x(2)+0.5*sin(x(4));
  v=2*sin(x(1)+pi/6)-x(3)-0.5*cos(x(4));
  w=2*sqrt(3)*(sqrt(3)*sin(x(1))+0.5)*cos(x(1))-...
    4*u*sin(x(1)+pi/6)+4*v*cos(x(1)+pi/6);
  A=[2*sqrt(3)*sin(x(1)),1,0,0; -2*sqrt(3)*cos(x(1)),0,1,0;
     -2*sqrt(3)*(sqrt(3)*cos(x(1))-0.5)*sin(x(1))+2*sqrt(3)*(sqrt(3)*sin(x(1))+0.5)*cos(x(1)),0,0,0;
     -4*u*sin(x(1)+pi/6)+4*v*cos(x(1)+pi/6), -2*u,-2*v, u*cos(x(4))+v*sin(x(4))];
  B=[0; 0; 0.4*(t/5+1.8); t/50+0.38]; dx=inv(A)*B;