How to stop, reset the variables and restart an ODE solver?

I am trying to solve a system of equations in which I want to stop the solver at certain t-values, reset the value of depenedent variables, and restart the solver. Is there an example that I can look at and try to mimic?

Answer 1

[Walter Roberson]

Look at ballode and how it uses "events", and observe how it loops calls until the entire time is complete.

[VR]

I could only find bounceEvents.m but not events.m. Any help will be appreciated.

[Walter Roberson]

Which release are you using? In R2019a, the function "events" is at the bottom of ballode.m

In any case, what I was referring to was not a specific function, but rather the Events option . In the version of ballode I am looking at now, close to the top of the file, a variable named options is assigned to using the result of calling odeset() with several parameters, the first of which is 'Events', @events . Perhaps in the version you are looking it it might say 'Events', @bounceEvents . The exact name of the function is not important: the importance is in the 'Events' option and the structure of the function that is called.

[VR]

Got it. Is it this one?

function [value,isterminal,direction] = events(t,y)
% Locate the time when height passes through zero in a decreasing direction
% and stop integration.
value = y(1);     % detect height = 0
isterminal = 1;   % stop the integration
direction = -1;   % negative direction

Now, if I want the integration to stop and reset the value of the first dependent variable at t=6 (say), do I edit the value or the isterminal?

Is there more documentation about these parameters? I feel like I don't understand how they work so I cannot edit them.

[Walter Roberson]

https://www.mathworks.com/help/matlab/math/ode-event-location.html

[VR]

Thanks but I had already looked at it. I still don't understand how I can adapt the following line so that it stops integrating at t=6 and replace dydt(2) to be 40 (say) and starts integrating again.

value = y(1);

I tried to replace it with the following but it doesn't seem to work.

value = t-6;