[R] Precision in R

[Huntsinger, Reid]

The summands can get pretty large: the 2^(2*r) factor will erase a lot of
precision. Is there another way to compute this? Perhaps use the recurrence
relation for the binomial coefficient to get a recurrence relation for your
function? 

Reid Huntsinger

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Francisco Fuentes
Sent: Thursday, May 05, 2005 2:02 PM
To: r-help at stat.math.ethz.ch
Subject: [R] Precision in R


Could anyone help me with the following issue.
Using the GSL library in R I define the following code:

#########
library(gsl);
S<-function(n)
{ r<-0:n;
ans<-sum(gsl_sf_choose(n,r)*(-1)^r*2^(2*r)*gamma_inc(6-2*r,2))
ans }
#########
>SS(10)   yields 34.91868
>SS(40)   yields 5.340422
>SS(60)   yields 180.3162
Doing the same computations in maple I get
 
34.918679360927169740821310620770402166885975646756
5.340473872869891061658721253647686930049562214921
2.2269219454888559341895277572725106
 
respectively.  Is this a precision problem?


		
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