- #1

- 1

- 0

Hi everybody,

I'm trying to solve this first-order ODEs system:and I'd like to stop the solution when y, i.e u(3), becomes negative:

I use ode45 as solver, and in order to stop it the option OutputFcn.

It stops after few values, when y is already positive.

Here is the script

Thank you all

Best Regards

I'm trying to solve this first-order ODEs system:and I'd like to stop the solution when y, i.e u(3), becomes negative:

Matlab:

```
%system
function rhs=particle(t,u)
global k
rhs=[u(2);
-k*u(1)*sqrt(u(2)*u(2)+u(4)*u(4));
u(4);
-9.81-k*abs(u(4))*sqrt(u(2)*u(2)+u(4)*u(4))];
where u(1)=x,u(2)=dx/dt,u(3)=y,u(4)=dy/dt
```

It stops after few values, when y is already positive.

Here is the script

Matlab:

```
%ode script
global k
t0=0;tend=10;
k=0.065;
a=20*pi/180;
u0=[0 20*cos(a) 1.5 20sin(a)];
options = odeset('OutputFcn',@output);
[time,result]=ode45('particle',[t0,tend],u0,options);
%output function
function status = output(t,y,status)
[val,pos]=min(y)
status=(val>=0)
if status==1
tend=t(pos);
end
```

Thank you all

Best Regards

Last edited by a moderator: