function plotce(mu,sig,n)
% plotce(mu,sig,n)
% mu: mean
% sig: cov

alpha=0.05;
len=100;
r=sqrt(5.9915); % 5.9915 is the chi^2 val. with 2 df. at 95%
[ev,e]=eig(inv(sig));
theta=linspace(0,2*pi,len);
xy=[cos(theta)./sqrt(e(1,1));sin(theta)./sqrt(e(2,2))];
el=(ones(len,1)*mu+r.*(ev*xy)')';
line(el(1,:),el(2,:))
  hold on;
plot(mu(1),mu(2),'ro')
