[R] Wrapper function for multivariate arrays for ode

[David Winsemius]

On Jul 2, 2012, at 10:09 PM, Tjun Kiat Teo wrote:

> I am trying to to write a wrapper function for the ode solver (under
> the package desolve) to enable it to take multivariate arrays. I know
> how to do it for 1 dimension arrays but my code breaks down when I try
> to do it for 2 dimensional arrays. Here is my code
>
>
> diffwrap<-function(t,y,mu)vdpol(t=t,A[1:3,1:4]<-y[1:12],B[1:12]<- 
> y[13:24],mu=mu)

I do not know whether this explains your problems , but it generally  
is very dangerous practice to have items in function argument lists  
like: A[1:3,1:4]<-y[1:12] and B[1:12]<-y[13:24]

I've often received similar messages when I mistaken entered "<-"  
rather than "=" in that situation.

The code runs with this definition (after loading pkg:deSolve rather  
than 'desolve'):

diffwrap<-function(t,y,mu) vdpol(t=t, A = matrix(y[1:12], 3,4),  
B=y[13:24], mu=mu)

Whether the output is sensible mathematically is beyond my knowledge,

-- 
David

>
> vdpol<-function(t,A,B,mu)
> {
> list(c(mu,
>       2,
>       3,
>       4,
>       5,
>       6,
>       7,
>       8,
>       9,
>       10,
>       11,
>       12,
>       A[1,1],
>       A[2,1],
>       A[3,1],
>       A[1,2],
>       A[2,2],
>       A[3,2],
>       A[1,3],
>       A[2,3],
>       A[3,3],
>       A[1,4],
>       A[2,4],
>       A[3,4])
>      )
> }
>
> stiff<-ode(y=rep(0,24),times=c(0,1),func=diffwrap,parms=1)
>
>
> I get keep getting the error message variable A[1,1] not found.
>
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David Winsemius, MD
West Hartford, CT