function plot_level(I, u ,i)
% Show zero level set of function u over image I
% Optionally, pass an integer argument, i, for number of iterations  
imshow(I,'initialmagnification','fit','displayrange',[0 1]);
hold on;
contour(u, [0 0], 'r','LineWidth',1);
hold off; 
if(nargin==3)
	title([num2str(i) ' Iterations']);
else
	title('Zero level set');
end 
drawnow;
