anonymous function in ode45: column vector error

To solve ODE below with matlab

t = 0:.01:20;
x0 = [0 0]';
xdot = @(t,x) [0 1; 0 0] * x;
ode45(@(t,x) xdot(x(1), x(2)),t,x0)
    

I get this error:

Error using odearguments (line 91) @(T,X)XDOT(X(1),X(2)) must return a column vector.

Cloud anyone help me to solve solve 2nd order ODEs using only anonymous function definition?

Answer 1

[Star Strider]

You are not calling ‘xdot’ correctly in your ode45 call.

Try this:

t = 0:.01:20;
x0 = [0 0]' + eps;
xdot = @(t,x) [0 1; 0 0] * x;
[T,X] = ode45(xdot,t,x0)


figure
plot(T, X)
grid

Also, the result is uniformly zero, so to prevent that, I added eps to ‘x0’.