Re: [R] Arbitrary Precision Numbers

From: jim holtman <jholtman_at_gmail.com>
Date: Fri, 04 Apr 2008 20:26:31 -0500

One way of "doing it in R" is to use the 'bc' command that is on most UNIX/LINUX systems and is also on cygwin for Windows. Here are decimal digits for 2^1000

/cygdrive/c/jph/consulting/2008-03-30: bc bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc. This is free software with ABSOLUTELY NO WARRANTY. For details type `warranty'.
2^1000

10715086071862673209484250490600018105614048117055336074437503883703\
51051124936122493198378815695858127594672917553146825187145285692314\
04359845775746985748039345677748242309854210746050623711418779541821\
53046474983581941267398767559165543946077062914571196477686542167660\
429831652624386837205668069376

So you can 'shell' the command from R, collect the digits and then sum them.

On Fri, Apr 4, 2008 at 10:43 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.
>
> ______________________________________________
> R-help_at_r-project.org mailing list
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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>

-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?

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Received on Sat 05 Apr 2008 - 01:32:01 GMT

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