R help - Feb 2010 - 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
 

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