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

[Ben Bolker]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1



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])


-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.6 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFIoHiVc5UpGjwzenMRAs+DAJ9kekwPnnlVE8mAMa61OmCkl0E2fACgiCy3
L/oQ3zIonFXAcGmvugXjTdE=
=GQFi
-----END PGP SIGNATURE-----