[R] using LSODA in R

[Ivan Kautter]

Thanks for the response, Ben.

It's not a case that the list isn't coming out correctly.  It's that the 
numbers that are coming out are not the numbers that these equations should 
be producing if I have specified the equations correctly in R code for use 
with LSODA.  So the question is more if I have the code right when the user 
specifies the differential equations for LSODA.


>From: Ben Bolker <bolker at zoo.ufl.edu>
>Reply-To: bolker at zoo.ufl.edu
>To: Ivan Kautter <ivankautter at hotmail.com>
>CC: R help list <r-help at stat.math.ethz.ch>
>Subject: Re: [R] using LSODA in R
>Date: Wed, 5 Nov 2003 08:43:53 -0500 (EST)
>
>
>   Try returning list(c(Rprime,Cprime,Pprime),NULL) -- the first element in
>the returned list should be a numeric *vector* of the derivatives.
>
>   Ben
>
>On Tue, 4 Nov 2003, Ivan Kautter wrote:
>
> > R help list subscribers,
> >
> > I am a new user of R.  I am attempting to use R to explore a set of
> > equations specifying the dynamics of a three trophic level food chain.  
>I
> > have put together this code for the function that is to be evaluted by
> > LSODA.  My equations Rprime, Cprime, and Pprime are meant to describe 
>the
> > actual equation of the derivative.  When I run LSODA, I do not get the
> > output that these equations should be giving.  Can someone tell me if I 
>have
> > set this function up correctly to use with LSODA when the user is 
>specifying
> > the equation of the derivative  or offer some advice for using LSODA in 
>R?
> > An example of how to code for user specified differential equations 
>would be
> > great.
> >
> > function(times,y,p)
> > {
> > Rprime <-
> > (R*(1-R))-((xc*yc*C*R)/(R+R0))-((w*xp*ypr*P*R)/(R02+((1-w)*C)+(w*R)))
> > Cprime <-
> > (-1*(xc*C)*(1-(yc*R)/(R+R0)))-(((1-w)*xp*ypc*P*C)/((w*R)+((1-w)*C)+C0))
> > Pprime <-
> > 
>(-1*P)-(((1-w)*xp*ypc*C*P)/((w*R)+((1-w)*C)+C0))+((w*xp*ypr*P*R)/((w*R)+((1-w)*C)+R02))
> > list(c(Rprime, Cprime, Pprime))
> > }
> >
> > The above is the function yprime which the documentation for the 
>odesolve
> > says that I may specify.
> >
> > Thanks for any help that anyone can provide.
> >
> > Ivan Kautter
> >
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>
>--
>620B Bartram Hall                            bolker at zoo.ufl.edu
>Zoology Department, University of Florida    http://www.zoo.ufl.edu/bolker
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