R help - Jan 2010 - problem with the precision of numbers

Hi All,

I was wodering if it is possible to increase the precision using R. I ran
the script below in R and MAPLE and I got different results when k is large.
Any idea how to fix this problem? thanks for your help


for (k in 0:2000){
 s=0
 for(i in 0:k){
 s=s+((-1)^i)*3456*(1+i*1/2000)^3000
 }
}
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kayj <kjaja27 <at> yahoo.com> writes:
> 
> 
> Hi All,
> 
> I was wodering if it is possible to increase the precision using R. I ran
> the script below in R and MAPLE and I got different results when k is
large.
> Any idea how to fix this problem? thanks for your help
> 
> for (k in 0:2000){
>  s=0
>  for(i in 0:k){
>  s=s+((-1)^i)*3456*(1+i*1/2000)^3000
>  }
> }

(1) see
http://wiki.r-project.org/rwiki/doku.php?id=misc:r_accuracy:high_precision_arithmetic

(2) consider whether there is more accurate algorithm you
could use. I don't recognize the series, but perhaps it
has a closed form solution, maybe as a special function?
How much accuracy do you really need in the solution?

  Ben Bolker

Maybe bc(..., args = "") or perhaps install a more standard version of
bc. See links at http://r-bc.googlecode.com

On Tue, Jan 19, 2010 at 5:43 PM, kayj <kjaja27 at yahoo.com>
wrote:
>
> Hi ,
>
> Thanks for your help, I have been trying to use the bc package but I am
> getting the following error
>
> "Error in system(cmd, input = input, intern = TRUE) : -l not
found"
>
>
> any idea??
>
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> View this message in context:
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>
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> and provide commented, minimal, self-contained, reproducible code.
>

Hi All,

I was wondering if R can deal with high precsion numbers, below is an
example that I tried on using R and Maple where I got different results. I
was not able to use the r-bc package in R, instead I used the Rmpfr
package, below are both R and Maple results

> library(Rmpfr) 
> 
> s<-mpfr(0,500)
> j <- mpfr(-1,500)
> 
> for (i in 0:80){ 
+ p<-as.numeric(i)
+ c<-choose(80,i)
+ s=s+((j^i)*c*(1-(i+1)*1/200)^200)
+  
+ }
> s
1 'mpfr' number of precision  500   bits 
[1]
4.6484825769379918039202329231788093343835337105287241996630873753794810915791302829474613042869191092322033403649086087872119205043462728841279067042348e-6


Maple result

6.656852479*10^(-20)


why are the two results different?

I appreciate your help




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