function eye_diag(x)
%	eye_diag(x)
% generate eye_diagram, for 
% x=[clock period in samples ,signal row vector]
	clk=x(1);
	L=length(x)-1;b=floor(2*clk);
	t=[1:b];N=floor((L-b)/clk)-1;
	M=floor(N/4);
	y=zeros(N-M+1,b);
	for k=[M:N]
		y(k-M+1,:)=x(k*clk+t);
	end
	mn=min(x);mx=max(x(2:L));
	plot(t,y)
	axis([1,b,mn,mx])
	axis('off')