Make lsoda terminate once state variable reacjes a threshold value

Question

As a toy example, consider the differential equation, dx / dt = p x

  ODE = function(t, X, p){ list( p*X ) }  

One can solve this using lsoda from package deSolve with no problem.

  times = seq(0, 20, by=.1)
  out = lsoda( y = 1, times, ODE, p = 2 )

However, I'd like lsoda to stop computing after a threshold value has been reached, say xMax = 1e5. I coudn't seem to find this option in the documentation. There is an option for events which looks promising for possibly implementing something like this.

Answer 1

In the deSolve documentation for lsoda you can also find the rootfunc parameter which can be used to trigger an event at root locations.

See example 3 in https://www.rdocumentation.org/packages/deSolve/versions/1.10-9/topics/events for an example that seems very close to your test case.