Phase Plot - Velocity vs Position

How can I create a graph of velocity vs position(x' vs x) (phase plot).

Here is the current code I am working with..

function LAB08ex1

m = 1; %mass [kg]

k = 4; %spring constant [N/m]

omega0 = sqrt(k/m);

y0 = 0.1; v0 = 0; %initial conditions

[t,Y] = ode45(@f,[0,10],[y0,v0],[],omega0); % solve for 0<t<10

y = Y(:,1); v = Y(:,2); % time series for y and v

E = (1/2*m*v.^2)+(1/2*k*y.^2); %calculating the energy

figure(1); plot(t,y, 'b+-',t,v,'ro-', t,E, 'gro-'); % retrieve y, v from Y

%-----------------------------------------x

function dYdt = f(t,Y,omega0)

y = Y(1); v = Y(2);

dYdt = [ v ; -omega0^2*y ];

Answer 1

[Star Strider]

Unless I am not understanding your code, that would appear to be:

figure(2)
plot(y, v)
grid
xlabel('Position')
yleabel('Velocity')