Splitting a position vector into X & Y then plotting them

Below is a function of position for a Simple Rocket that is losing mass due to fuel, Thrust is constant and a few other variables. I believe the " f " is the Y component and the y is the input x component. I am trying to save to .dat file the X Vector and the Y Vector, and then plot an Y(t) vs X(t). I can't seem to figure out how to do so, can I get some help?

%y=[x;y;x';y']

f=@(t,y) [y(3:4);-1/(2*m)*rho*Cd*S*norm(y(3:4))*y(3:4)-[0;g]];

fps = 60;

tspan = 0:1/10:20;

% vx0=0.01; %X velocity initial

% vy0=1; %Y velocity initial

y0=[0;0;v0;v0]; %Position, Xi Yi X'i Yi

[t,y] = ode45(f,tspan,y0);

save HW7_10.dat y -ascii

save HW7_11.dat f -ascii

% figure

% plot(x,y)

% title('Y(t) vs. X(t)')

figure

title('Y(t) vs. X(t)')

plot([y(end) y], [f(end) f], 'r-');

Answer 1

[Alan Stevens]

Soething like this (needs your data to get a sensible solution):

m = 1; rho = 1; Cd = 1; S = 1; g = 9.8; % Replace with your values
f=@(t,y) [y(3:4);-1/(2*m)*rho*Cd*S*norm(y(3:4))*y(3:4)-[0;g]];
fps = 60;
tspan = 0:1/10:20;
vx0=0.01; %X velocity initial
vy0=1;  %Y velocity initial
y0=[0;0;vx0;vy0]; %Position, Xi Yi X'i Yi
[t,y] = ode45(f,tspan,y0);
X = y(:,1);
Y = y(:,2);
plot(X,Y)