function sol = prob_4_6
% 
% Written by:
% -- 
% John L. Weatherwax                2005-04-25
% 
% email: wax@alum.mit.edu
% 
% Please send comments and especially bug reports to the
% above email address.
% 
%-----
  
options = ddeset( 'RelTol', 1e-9, 'InitialY', [ 0 0 ] );

sol = dde23(@ddes,[1,2],@history,[0, 4]);
plot(sol.x,sol.y(1,:),'-o'); grid on; 

function v = history(t)

v = [ cos(t); sin(t) ];

function dydt = ddes(t,y,Z)

dydt = [ Z(1,1)*Z(2,2); 
         -y(1)*Z(2,2); ];