[R] Help with Iterator

[Daniel Nordlund]

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
> On Behalf Of zhiji19
> Sent: Tuesday, November 09, 2010 12:02 AM
> To: r-help at r-project.org
> Subject: [R] Help with Iterator
> 
> 
> Dear Experts,
> 
> The following is my "Iterator". When I try to write a new function with
> itel, I got error.
> 
> This is what I have:
> > supDist<-function(x,y) return(max(abs(x-y)))
> >
> > myIterator <- function(xinit,f,data=NULL,eps=1e-6,itmax=5,verbose=FALSE)
> {
> + xold<-xinit
> + itel<-0
> + repeat {
> +   xnew<-f(xold,data)
> +   if (verbose) {
> +     cat(
> +     "Iteration: ",formatC(itel,width=3, format="d"),
> +     "xold: ",formatC(xold,digits=8,width=12,format="f"),
> +     "xnew: ",formatC(xnew,digits=8,width=12,format="f"),
> +     "\n"
> +     )
> +     }
> +     if ((supDist(xold,xnew) < eps) || (itel == itmax)) {
> +       return(xnew)
> +     }
> +   xold<-xnew; itel<-itel+1
> +   }
> + }
> 
> > mat<-function (x, data=NULL) {return (1+x^itel)}
> > myIterator(3, f=mat, verbose=TRUE)
> Error in f(xold, data) : object 'itel' not found
> 
> 
> Can anyone please help me to fix the error?

It appears to me that your problem is a matter of variable "scope".  The error message says that the function f cannot find object 'itel'.  That is because itel is defined in the function iterate and is local to that function.  You might want to add a third parameter to function f so you can pass in the value of itel.  (I would avoid using itel for the parameter name as you will likely end up confusing yourself at some point).  I haven't tried to figure out what you are doing so I don't know if that is the best solution. But the problem is that f doesn't know about object 'itel'.    

Hope this is helpful,

Dan

Daniel Nordlund
Bothell, WA USA