Making my simulation stop when z=0

I need a way to tell my plot to stop when z=0. Right now it keeps going into the negative z direction until it hits my time that I have it set to. Here is my code

tspan = [0, 30];
IC = [0, 91.8559, 0, 91.8559, 0, 86.6025]
[time, state_values] = ode45(@project12,tspan,IC);
x = state_values(:,1);
xdot = state_values(:,2);
y = state_values(:,3);
ydot=state_values(:,4);
z = state_values(:,5);
zdot=state_values(:,6);
%plot x(t)
subplot(3,1,1)
plot(time,x)
%plot y(t)
subplot(3,1,2)
plot(time,y)
%plot z(t)
subplot(3,1,3)
plot(time,z)
function sdot = project12(t,s)
% s eqauls x, xdot, y, ydot, z, zdot 
sdot(1)=s(2)
sdot(2)=0
sdot(3)=s(4)
sdot(4)=0
sdot(5)=s(6)
sdot(6)=-9.81
sdot=sdot'
end

Answer 1

[Walter Roberson]

You would use an event function.

I recommend looking at the ballode example, as it does this kind of processing.

[Stephen Mixon]

I looked at the mathworks page for this. How would I implement this in my code

[Walter Roberson]

Copy ballode to a new file . Change the function name on the first line. Change

for i = 1:10

to

for i = 1:1

Change function f to your actual function.

That should pretty much do it.