[R] using LSODA in R

[Ben Bolker]

  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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