From brian at braverock.com  Mon Nov 21 15:58:01 2011
From: brian at braverock.com (Brian G. Peterson)
Date: Mon, 21 Nov 2011 08:58:01 -0600
Subject: [Rd] a^b when a is large and b < 1 (64bit R on windows 7)
In-Reply-To: <49E76DF37649DC48A4CE882BC8CE51C901F44592@nagmail2.nag.co.uk>
References: <49E76DF37649DC48A4CE882BC8CE51C901F44592@nagmail2.nag.co.uk>
Message-ID: <1321887481.29526.14.camel@brian-rcg>

On Mon, 2011-11-21 at 14:41 +0000, Martyn Byng wrote:
> I'm getting some strange behaviour when trying to use the power
> operator
> (a^b) when a is large and b is less than one:
> 
> big <- .Machine$double.xmax
> big
> big^0.5
> sqrt(big)
> 
> > big <- 1.797693134862315708384e+308
> > big^0.5
> [1] Inf
> > sqrt(big)
> [1] 1.340781e+154
> 
> 
> I'm guessing that this behaviour is not expected, or am I missing
> something about ^? 

On a recent Ubuntu 64bit install with R2.14.0 from the repositories, I
get:

> big <- .Machine$double.xmax
> big
[1] 1.797693e+308
> big^0.5
[1] 1.340781e+154
> sqrt(big)
[1] 1.340781e+154

so it does seem to be specific either to your environment.

-- 
Brian G. Peterson
http://braverock.com/brian/
Ph: 773-459-4973
IM: bgpbraverock



[Rd] a^b when a is large and b < 1 (64bit R on windows 7)
Brian G. Peterson