[R] Differential Equations there use in R (population modeling)

[stephen sefick]

thanks

On Mon, Aug 11, 2008 at 2:18 PM, Ben Bolker <bolker at ufl.edu> wrote:
>
>  There was a spurious tilde in the code coming
> from my digital signature -- oops.  ignore the
> tilde in the function:
>
> library(odesolve)
>
> ## in general x, b are state and parameter VECTORS
> e1B <- function(t,x,b) {
>    list(x*b^t,NULL)
> }
>
> L1 = lsoda(y=1,times=seq(0,1,by=0.02),func=e1B,parms=c(b=0.9))
> plot(L1[,1],L1[,2])
>
>
> stephen sefick wrote:
>>
>> error in isoda(y = 1, times = seq(0, 1, by = 0.02), func = e1B, parms
>> = c(b = 0.9)) :
>>  Model function must return a list
>>
>> this is the error message I get when I try and paste in the code.
>>
>> Stephen Sefick
>>
>> On Mon, Aug 11, 2008 at 1:36 PM, Ben Bolker <bolker at ufl.edu> wrote:
>>
>>
>> stephen sefick wrote:
>> | population# = (initialvalue @ t) - (death rate) + (fecundtity per
>> individual) dt
>> | to be able to vary the values of the inputs death rate and fecundity
>> | with time using initial value @ t from the previous time step to
>> | evaluate the function at the present time step.
>> |
>> | On Mon, Aug 11, 2008 at 9:43 AM, Ben Bolker <bolker at ufl.edu> wrote:
>> |> stephen sefick <ssefick <at> gmail.com> writes:
>> |>
>> |>> e1 <- function(x,b,t){
>> |>>       d<-(x)*(b^t)
>> |>>       plot(d)
>> |>> }
>> |>>
>> |>> e1(2, 2,seq(from=0, to=6, by=1))
>> |>>
>> |>> Is there a way to do this with a change in time.  I would like to use
>> |>> differential equations.
>> |>  I'm not sure what you mean by "do this with a change in time",
>> |> but in general for ODEs you should check out lsoda in the odesolve
>> package.
>> |> You can also look at the ecology/environment task view.
>> |>
>> |>  Ben Bolker
>> |>
>>
>> ~  Something like:
>>
>>
>> library(odesolve)
>>
>> ## in general x, b are state and parameter VECTORS
>> e1B <- function(t,x,b) {
>> ~    list(x*b^t,NULL)
>> }
>>
>> L1 = lsoda(y=1,times=seq(0,1,by=0.02),func=e1B,parms=c(b=0.9))
>> plot(L1[,1],L1[,2])
>>
>>
>>>
>
>



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