R help - Sep 2010 - ERROR: Object not found

Dear All,

 

I am trying to use ode solver "rk4" to solve an ODE system, however,
it
keeps saying: Error in eval(expr, envir, enclos) : object "dIN" not
found.
The sample codes are enclosed as follows, please help me. Thank you very
much!

 

rm(list=ls())

 

library(odesolve)

 

# The ODE system

ode <- function(t,x,p){

 

  with(as.list(c(x,p)),{

     

     if(IN==0){

       dIN <- 1

       switch <- c

     }

     else {

       switch <- 0

     }

 

     dP1 <- a+b*P1-switch*P1

     dP2 <- a-b*P1+switch*P2

 

  list(c(dP1,dP2,dIN)) 

  })

}

 

# Parameters

a <- 0.1

b <- 0.2

c <- 0.5

 

parms <- c(a=a,b=b,c=c)

 

# Initial conditions

P10 <- 100.0

P20 <- 0.0

IN0 <- 0.0

 

xstart <- c(P1=P10,P2=P20,IN=IN0)

 

# Time points

times <- seq(0,10,by=1)

 

out <- as.data.frame(rk4(xstart,times,ode,parms))


	[[alternative HTML version deleted]]

Error originates in the customized function ode. When IN!=0, You did 
not assign a value to dIN which is required in list(c(dP1,dP2,dIN)).

On 2010-9-21 2:30, Tianchan Niu wrote:
> Dear All,
>
>
>
> I am trying to use ode solver "rk4" to solve an ODE system,
however, it
> keeps saying: Error in eval(expr, envir, enclos) : object "dIN"
not found.
> The sample codes are enclosed as follows, please help me. Thank you very
> much!
>
>
>
> rm(list=ls())
>
>
>
> library(odesolve)
>
>
>
> # The ODE system
>
> ode<- function(t,x,p){
>
>
>
>    with(as.list(c(x,p)),{
>
>
>
>       if(IN==0){
>
>         dIN<- 1
>
>         switch<- c
>
>       }
>
>       else {
>
>         switch<- 0
>
>       }
>
>
>
>       dP1<- a+b*P1-switch*P1
>
>       dP2<- a-b*P1+switch*P2
>
>
>
>    list(c(dP1,dP2,dIN))
>
>    })
>
> }
>
>
>
> # Parameters
>
> a<- 0.1
>
> b<- 0.2
>
> c<- 0.5
>
>
>
> parms<- c(a=a,b=b,c=c)
>
>
>
> # Initial conditions
>
> P10<- 100.0
>
> P20<- 0.0
>
> IN0<- 0.0
>
>
>
> xstart<- c(P1=P10,P2=P20,IN=IN0)
>
>
>
> # Time points
>
> times<- seq(0,10,by=1)
>
>
>
> out<- as.data.frame(rk4(xstart,times,ode,parms))
>
>
> 	[[alternative HTML version deleted]]
>
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