[R-sig-dyn-mod] deSolve events - different event functions at different times

[Faelens Ruben]

Dear Tom,

We are using the root finding function of deSolve to fire multiple events at specific times.
Simply add an extra ODE that starts at t0 and has a derivative value of '1'.
You can then use a root function that returns 't - c(1, 2)' to fire an event at t=1 and t=2.

Your event function will look like this:
eventfun <- function(t, x, parms) {
    if(abs(t-1) < absolutePrecision) eventfun1(t, x, parms)
    if(abs(t-2) < absolutePrecision) eventfun2(t, x, parms)
}

It's ugly, but it works! The advantage is that you can add new event times while the solver is running (i.e. from within an event).

@List: I am very open to alternative suggestions that depend less on the precision of the solver though...

Ruben FAELENS 
Consultant
Altran Belgium

-----Original Message-----
From: r-sig-dynamic-models-bounces at r-project.org [mailto:r-sig-dynamic-models-bounces at r-project.org] On Behalf Of Tom.Sumner at lshtm.ac.uk
Sent: vrijdag 25 januari 2013 16:06
To: r-sig-dynamic-models at r-project.org
Subject: [R-sig-dyn-mod] deSolve events - different event functions at different times

Dear list, 

I am using deSolve to solve a set of ODEs and am trying to make use of the events mechanism. Is there a way to apply two different events (defined as functions) at different times?

Using an example from the inside-R documentation to illustrate:

# Derivative function
derive <- function(t, var, parms){
                  list(c(0,-0.5 *var[2])) }

# events
event1 <- function(t,y,parms){
with (as.list(y),{
v1 <- v1 + 1
v2 <- 5 * runif(1)
})
}

event2 <- function(t,y,parms){
with (as.list(y),{
v1 <- v1 + 0.5*y2
v2 <- 5 * runif(1)
})
}

yini <- c(v1  = 1, v2 = 2)
times <- seq(0, 10, by 0.1)

out <- ode(func = derivs, y =yini, times = times, parms = NULL,
  events = list(func = event1, time = 1)

The above would call event1 at time=1. Is there a way to also call event2 at a different time?

I am relatively new to R so apologies if I am missing something obvious.

Many thanks, 

Tom



   

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