%{
m-file to solve the system version of 
y"+9y=-1.  Solves for 0<t<6.  Period is
2*pi/3 ~ 2.

The last input is the initial data Y(0),Y'(0). 
%}

[T,Y]=ode45(@gravityspring , [0  6], [1 ; 0]);

 plot(T,Y(:,1))  %plots y(t) versus t
 
 %plot(T,Y)   %plots y(t) AND y'(t) versus t
 
 %plot3(T,Y(:,1),Y(:,2))  gives a threeD plot of y(t),y'(t) versus t.