ses around tips of pendulum (if M, S exist)
try
  if max(max(S))>0
    err = linspace(-1,1,100)*sqrt(S(2,2));
    plot(l*sin(M(2)+2*err),-l*cos(M(2)+2*err),'b','linewidth',1)
    plot(l*sin(M(2)+err),-l*cos(M(2)+err),'b','linewidth',2)
    plot(l*sin(M(2)),-l*cos(M(2)),'b.','markersize',20)
  end
catch
end

% Draw useful information
% target location
plot(0,l,'k+','MarkerSize',20);
plot([xmin, xmax], [-height, -height],'k','linewidth',2)
% joint
plot(0,0,'k.','markersize',24)
plot(0,0,'y.','markersize',14)
