R help - Feb 2010 - Fwd: Recall function: "evaluation nested too deeply: infinite recursion / options(expressions=)?"

hello all
 
i searched the archives and couldn't get a solution to the following
question.
 
i have the following function:
 
F=function(z,v)
{
  if (v==-.5) return(1) else  return(2*v/z + 1/Recall(z,v-1))
}
 
and while testing whether it works (ie F(z,v) is approx = 
besselK(z,1+v)/besselK(z,V). the recursion formula allows one to calculate
besselK(z,1+v)/besselK(z,V) for large values of z ) i got the following error :
"evaluation nested too deeply: infinite recursion /
options(expressions=)?"
 
i.e. 
zz=1
nn=1000

R=array(0,dim=nn)
for (i in 1:nn)
{
  print(i)
  R[i]=F(zz,-0.5+(i-1))
}
the error occurs when i==713
but when one evaluates F(1,-.5+(713-1)) i get [1] 1423.001
note also that if v starts getting large, evaluation of F also gives the error.
e.g. F(1, 713.5)
 
any help?
 
 
seems like looping works nicely here
 
F2=function(z,v)
{
  #check that the v is correct! ie -.5, .5, 3/2, 5/2, .....
  
  if (v==-0.5)
  {
    return(1)
  }else
  {
    ntimes = v+1.5
    R=array(0,dim=ntimes)
 
    R[1]=1
    for (i in 2:ntimes)
    {
      R[i]= 2*v/z + 1/R[i-1]
    }
    return(R[ntimes])
  }
}

 

 
 
 
Allan Clark
=======Lecturer in Statistical Sciences Department
University of Cape Town
7701 Rondebosch
South Africa
TEL (Office): +27-21-650-3228
FAX: +27-21-650-4773
http://web.uct.ac.za/depts/stats/aclark.htm
 
 
 
Allan Clark
=======Lecturer in Statistical Sciences Department
University of Cape Town
7701 Rondebosch
South Africa
TEL (Office): +27-21-650-3228
FAX: +27-21-650-4773
http://web.uct.ac.za/depts/stats/aclark.htm
 

	[[alternative HTML version deleted]]

You might be impacted by FAQ 7.31.

Your statement      if(v == -.5)

might be suspect.  You might want to use 'all.equal'

On Thu, Feb 11, 2010 at 11:40 AM, Allan Clark <Allan.Clark at uct.ac.za>
wrote:
> hello all
>
> i searched the archives and couldn't get a solution to the following
question.
>
> i have the following function:
>
> F=function(z,v)
> {
> ?if (v==-.5) return(1) else ?return(2*v/z + 1/Recall(z,v-1))
> }
>
> and while testing whether it works (ie F(z,v) is approx =
?besselK(z,1+v)/besselK(z,V). the recursion formula allows one to calculate
besselK(z,1+v)/besselK(z,V) for large values of z ) i got the following error :
"evaluation nested too deeply: infinite recursion /
options(expressions=)?"
>
> i.e.
> zz=1
> nn=1000
>
> R=array(0,dim=nn)
> for (i in 1:nn)
> {
> ?print(i)
> ?R[i]=F(zz,-0.5+(i-1))
> }
> the error occurs when i==713
> but when one evaluates F(1,-.5+(713-1)) i get [1] 1423.001
> note also that if v starts getting large, evaluation of F also gives the
error. e.g. F(1, 713.5)
>
> any help?
>
>
> seems like looping works nicely here
>
> F2=function(z,v)
> {
> ?#check that the v is correct! ie -.5, .5, 3/2, 5/2, .....
>
> ?if (v==-0.5)
> ?{
> ? ?return(1)
> ?}else
> ?{
> ? ?ntimes = v+1.5
> ? ?R=array(0,dim=ntimes)
>
> ? ?R[1]=1
> ? ?for (i in 2:ntimes)
> ? ?{
> ? ? ?R[i]= 2*v/z + 1/R[i-1]
> ? ?}
> ? ?return(R[ntimes])
> ?}
> }
>
>
>
>
>
>
> Allan Clark
> =======> Lecturer in Statistical Sciences Department
> University of Cape Town
> 7701 Rondebosch
> South Africa
> TEL (Office): +27-21-650-3228
> FAX: +27-21-650-4773
> http://web.uct.ac.za/depts/stats/aclark.htm
>
>
>
> Allan Clark
> =======> Lecturer in Statistical Sciences Department
> University of Cape Town
> 7701 Rondebosch
> South Africa
> TEL (Office): +27-21-650-3228
> FAX: +27-21-650-4773
> http://web.uct.ac.za/depts/stats/aclark.htm
>
>
> ? ? ? ?[[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?