Population values not updating in deSolve in R

问题

I am working on a model with different compartments for different age groups and smokers/non-smokers. I thought all was going well, but when I started to dig into the output, I see that the populations are not updating at each time step as I anticipated. I used the debugger to step through the code, and indeed, it keeps using the initial stock size for every time step, so I end up with a constant change in population sizes, which is incorrect.

There are 200 stocks in the model, so I don't want to paste the whole thing in, but here are the pieces I think may be most relevant.

smokdiff <- function(times,init,parameters) {
  with(as.list(c(init,parameters)), {

    dns00 <- births - ns00*mort[1,1] - ns00/5 
    dns05 <- ns00/5 - ns05*mort[1,2] - ns05/5

...

    list(c(dns00,dns05,dns10,...
 })
}

times <- seq(0,tf,dt)
init <- c(ns00,ns05,ns10,...
parameters <- c(births,mort,init15,utinit15,ltinit15)
out <- ode(func=smokdiff, times=times, y=init, parms=parameters)

Here is a sample of the output for the ns00 population:

     time       1
[1,]    0 9244769
[2,]    1 9217034
[3,]    2 9189300
[4,]    3 9161566
[5,]    4 9133832
[6,]    5 9106097

As you can see, it decreases by ~27,734 each step, which is only correct for the first step (e.g. it's supposed to decrease by 22,104 in the second step).

I have compared to multiple models I've found online, and I can't spot what it is I'm doing wrong. I've also tried other "methods" in the ode call, but they all display the constant change. I'm beginning to worry that I have some basic misunderstanding about how this is supposed to work. Can anyone see what I'm doing wrong? Thank you!

SOLUTION: The initial states have to be defined in a 'state=value' manner. Simply putting a variable with the value in it is insufficient. Here is a small working example:

library(deSolve)
smokdiff <- function(times,init,parameters) {
  with(as.list(c(init,parameters)), {

    dns00 <- births - ns00*mort[1] - ns00/5 
    dns05 <- ns00/5 - ns05*mort[2] - ns05/5
    dns10 <- ns05/5 - ns10*mort[3] - ns10/5

    list(c(dns00,dns05,dns10))
 })
}

mort <- c(0.003, 0.001, 0.001)
ns00 <- 9000000; ns05 <- 8500000; ns10 <- 8500000
births <- ns00/5
times <- seq(0,50,0.25)
init <- c(ns00=ns00,ns05=ns05,ns10=ns10)
parameters <- c(births,mort)
out <- ode(func=smokdiff, times=times, y=init, parms=parameters)

来源：https://stackoverflow.com/questions/27369877/population-values-not-updating-in-desolve-in-r

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ode