function sol = prob_4_4
% 
% Written by:
% -- 
% John L. Weatherwax                2005-05-07
% 
% email: wax@alum.mit.edu
% 
% Please send comments and especially bug reports to the
% above email address.
% 
%-----
  
sol = dde23(@ddes,14,0.5,[0, 300]);
t = linspace(50,300,1000);
y = deval(sol,t);
ylag = deval(sol,t - 14);
plot(y,ylag,'-o')
xlabel('y(t)');
ylabel('y(t - 14)');
%=================================
function dydt = ddes(t,y,Z)
dydt = 0.2*Z/(1 + Z^10 - 0.1*y);