[R] How to change parameter values as a function to time with the package "deSolve"

[David Winsemius]

> On Mar 23, 2017, at 2:59 PM, Marine Regis <marine.regis at hotmail.fr> wrote:
> 
> Hello,
> 
> I am trying to solve an ODE in R using deSolve. With the following code, I expected the parameter �gamma0� takes the values 5 at time step 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10, and 0 otherwise. However, the print(gamma0) shows that �gamma0� stays at 0.
> 
> Here is my ODE:
> 
> param <- c(a = 0.1, b = 1)
> yini <- c(alpha0 = 0, beta0 = 0)
> 
> mod <- function(times, yini, param) {
> 
>  with(as.list(c(yini, parameters)), {
> 
>  gamma0 <- ifelse(times %in% seq(0,10,1), 5, 0)
> 
>  # print(gamma0)
> 
>  dalpha0 <- - a*alpha0 + gamma0
>  dbeta0 <- a*alpha0 - b*beta0
>  return(list(c(dalpha0, dbeta0)))
> 
>  })}
> 
> times <- seq(from = 0, to = 10, by = 1/24)
> out <- ode(func = mod, times = times, y = yini, parms = param)
> plot(out, lwd = 2, xlab = "day")
> 
> 
> What am I doing wrong? Thanks in advance for your help!

When I execute that code I get:

Error in as.list(c(yini, parameters)) : object 'parameters' not found

(The mistake seems fairly obvious when you look are the parameter list for your `mod` function.)

Additionally: It's not generally good practice to use `with` inside functions, but that's not the problem here.

-- 
David.

> Marine
> 
> 
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> 
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David Winsemius
Alameda, CA, USA