R help - Aug 2010 - Recursion problem

Hi,


I wanted to compute the value of the function ifn at certain values of n. But I 
am receiving the following error when I was using the following code(given at 
the end).

Error: evaluation nested too deeply: infinite recursion / options(expressions=)?
 
I feel that since the function Grx is recursively related, perhaps making the 
code too complicated too handle. Can anyone let me know if there is any other 
way to handle this problem? 


d1=10.5
Grx<-function(x,r)
{
G0=Grx(x,0)
G0=1;
fu1<-function(t){exp(-t^2/(2*r*(r+1)))*Grx(x,r-1)}
return(integrate(fu1,0,x)$value)
}

grx<-function(x,r)
{
Grx(x,r)*exp(-x^2/(2*(r+1)))
}

ifn<-function(n)
{
w=n*d1/2;S1=0;
for(k in  1:(n-1))
{
 S1=S1+choose(n,k)*grx(w,k)*grx(w,n-k-1)
}
return(S1);
}

ifn(7)

Thanks in advance.

Shant


      
	[[alternative HTML version deleted]]

We replied once that your function Grx is not correct.  It will
recurse to an infinite depth because there is no condition to end the
calls.  I would expect that there would be some test at the beginning
of the function to see if it should be called again.  You need to
debug your function, or rewrite to compute what you want.  You have
not described the problem you are trying to solve, so no solution can
be provided.

On Sun, Aug 22, 2010 at 12:03 AM, Shant Ch <sha1one at yahoo.com>
wrote:
>
>
> Hi,
>
>
> I wanted to compute the value of the function ifn at certain values of n.
But I
> am receiving the following error when I was using the following code(given
at
> the end).
>
> Error: evaluation nested too deeply: infinite recursion /
options(expressions=)?
>
> I feel that since the function Grx is recursively related, perhaps making
the
> code too complicated too handle. Can anyone let me know if there is any
other
> way to handle this problem?
>
>
> d1=10.5
> Grx<-function(x,r)
> {
> G0=Grx(x,0)
> G0=1;
> fu1<-function(t){exp(-t^2/(2*r*(r+1)))*Grx(x,r-1)}
> return(integrate(fu1,0,x)$value)
> }
>
> grx<-function(x,r)
> {
> Grx(x,r)*exp(-x^2/(2*(r+1)))
> }
>
> ifn<-function(n)
> {
> w=n*d1/2;S1=0;
> for(k in ?1:(n-1))
> {
> ?S1=S1+choose(n,k)*grx(w,k)*grx(w,n-k-1)
> }
> return(S1);
> }
>
> ifn(7)
>
> Thanks in advance.
>
> Shant
>
>
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Shant Ch
> Sent: Saturday, August 21, 2010 9:04 PM
> To: r-help at r-project.org
> Subject: [R] Recursion problem
> 
> 
> 
> Hi,
> 
> 
> I wanted to compute the value of the function ifn at certain 
> values of n. But I 
> am receiving the following error when I was using the 
> following code(given at 
> the end).
> 
> Error: evaluation nested too deeply: infinite recursion / 
> options(expressions=)?
>  
> I feel that since the function Grx is recursively related, 
> perhaps making the 
> code too complicated too handle. Can anyone let me know if 
> there is any other 
> way to handle this problem? 
> 
> 
> d1=10.5
> Grx<-function(x,r)
> {
> G0=Grx(x,0)
> G0=1;
> fu1<-function(t){exp(-t^2/(2*r*(r+1)))*Grx(x,r-1)}
> return(integrate(fu1,0,x)$value)
> }
Your keep calling Grz(x, r-1) forever, as r descends
from its starting value towards -Inf.  Are you try
to use the
     G0=Grz(x,0)
     G0=1
to say what to return when r==0 (vaguely like Haskell)?
If so the proper syntax would be
  Grx <- function (x, r) {
      retval <- if (r < 0) {
          # must r be integral?
          stop("r must be nonnegative")
      }
      else if (r == 0) {
          1
      }
      else {
          fu1 <- function(t) {
              exp(-t^2/(2 * r * (r + 1))) * Grx(x, r - 1)
          }
          integrate(fu1, 0, x)$value
      }
      # Uncomment next line to trace the recursion
      # cat("x=", x, ", r=", r, " -> ", retval,
"\n")
      retval
  }

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com  

> 
> grx<-function(x,r)
> {
> Grx(x,r)*exp(-x^2/(2*(r+1)))
> }
> 
> ifn<-function(n)
> {
> w=n*d1/2;S1=0;
> for(k in  1:(n-1))
> {
>  S1=S1+choose(n,k)*grx(w,k)*grx(w,n-k-1)
> }
> return(S1);
> }
> 
> ifn(7)
> 
> Thanks in advance.
> 
> Shant
> 
> 
>       
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>