RE: [R] Precision in R

From: Huntsinger, Reid <reid_huntsinger_at_merck.com>
Date: Fri 06 May 2005 - 04:18:50 EST


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@stat.math.ethz.ch
[mailto:r-help-bounces@stat.math.ethz.ch] On Behalf Of Francisco Fuentes Sent: Thursday, May 05, 2005 2:02 PM
To: r-help@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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R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri May 06 04:30:39 2005

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