%This is a function m-file to compute the solution of

% x''=4x(1-x^2)

% t in [0,10] x(0)=0 x'(0)=1

%written as a system for the vector [x(t,1), x(t,2)], where x(t,1)=x(t), x(t,2)=x'(t)]

function xprime=example5(t,x)

xprime=zeros(2,1);

xprime(1)=x(2);

xprime(2)=4*x(1)*(1-x(1)^2);

%Once this is saved as example5.m, the call to the ode solver would be:

%[t,x]=ode45(@example5, [0,10], [0;1])

%(the second argument is the time interval, the last argument is the column vector with the initial conditions)

%Then to plot both components (remember to quit pplane7 if it is open):

% plot(t,x)

%and to plot just the first component, that is, x(t):

% plot (t,x(:,1))