function drawvoronoi
a=[2.51; 2.23];
Q=[0.2767 0.2152; 0.2152 0.1680];

[z,f,Z]=lambda(a,Q,1); % z=Z'*Q,Qz=Z'*Q*Z
L=chol(Z'*Q*Z);

s=L'*randn(2,10000);
[z1,z2]=meshgrid(z(1)+(-4:4),z(2)+(-4:4));
x=L'\[z1(:)';z2(:)'];
[x1,x2]=voronoi(x(1,:),x(2,:));
v1=L'*[x1(1,:);x2(1,:)];
v2=L'*[x1(2,:);x2(2,:)];

gut('newfigg','','',[600,400]);
ggt('newaxes','',[0.08,0.1,0.84,0.8]);
axis equal
plot(z(1)+s(1,:),z(2)+s(2,:),'.','color',[.5,.5,.5],'markersize',1);
plot(z1,z2,'b.');
plot([v1(1,:);v2(1,:)],[v1(2,:);v2(2,:)],'b-');
set(gca,'xlim',[-2,4],'ylim',[-1,3],'xtick',-2:4,'ytick',-1:3);
title('pull-in regions of z=Z''*a'); xlabel('z1'); ylabel('z2');
