# [R] Arbitrary Precision Numbers

Gabor Grothendieck ggrothendieck at gmail.com
Sat Apr 5 04:01:45 CEST 2008

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On Fri, Apr 4, 2008 at 9:55 PM, Gabor Grothendieck
<ggrothendieck at gmail.com> wrote:
> Have a look at the Ryacas package which interfaces R to yacas.
> yacas can do exact arithmetic.
>
>
> On Fri, Apr 4, 2008 at 11:43 AM, Rory Winston <rory.winston at gmail.com> wrote:
> >
> > Hi
> >
> > (If you're wondering, this is a Project Euler question :))
> >
> > If I wanted to calculate the sum of the digits in the decimal representation
> > of 2^1000, what would be a good way to go about that? I've tried the
> > following methods:
> >
> > # Calculate the sum of digits in the decimal representation of 2^n
> > # Only works for smaller values of n
> > bsum <- function(n) {
> >        s <- 0
> >        e <- floor(log10(2^n))
> >        for (i in seq(e,0,-1)) {
> >                s <- s + (((2^n) %/% 10^i) %% 10)
> >        }
> >        s
> > }
> >
> > The above doesnt work, as I am using an integer modulus which has
> > insufficient precision. so I tried to coerce R to produce a full-precision
> > integer and sum the digits of that:
> >
> > bsum2 <- function(n) {
> >        s <- 0
> >        strn <- formatC(2^n, format="fg")
> >        sum(as.numeric(strsplit(strn,"")[[1]]))
> > }
> >
> > This also doesnt seem to work. Is there another way I can do this in R?
> > Cheers
> > Rory
> > --
> > View this message in context: http://www.nabble.com/Arbitrary-Precision-Numbers-tp16492549p16492549.html
> > Sent from the R help mailing list archive at Nabble.com.
> >
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