From jorismeys at gmail.com  Mon Nov 21 15:54:54 2011
From: jorismeys at gmail.com (Joris Meys)
Date: Mon, 21 Nov 2011 15:54:54 +0100
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: <CAO1zAVax2LL=wBmXHZFDGXrD_EnUU=06BmGJ-w_befQ=NYMKxQ@mail.gmail.com>

I can reproduce on the latest patched build, but this is specific for
the 64bit version of R. On a 32bit it works as expected:

> big <- 1.797693134862315708385e+308
> sqrt(big)
[1] 1.340781e+154
> big^0.5
[1] 1.340781e+154

The 64bit part might have something to do with it, and now move out of
the way for people that actually know what they're talking about...

Cheers
Joris


On Mon, Nov 21, 2011 at 3:41 PM, Martyn Byng <Martyn.Byng at nag.co.uk> wrote:
> Hi,
>
> 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 ^?
>
> Cheers
>
> Martyn
>
>
>
>> sessionInfo()
> R version 2.14.0 (2011-10-31)
> Platform: x86_64-pc-mingw32/x64 (64-bit)
>
> locale:
> [1] LC_COLLATE=English_United Kingdom.1252
> [2] LC_CTYPE=English_United Kingdom.1252
> [3] LC_MONETARY=English_United Kingdom.1252
> [4] LC_NUMERIC=C
> [5] LC_TIME=English_United Kingdom.1252
>
> attached base packages:
> [1] stats ? ? graphics ?grDevices utils ? ? datasets ?methods ? base
>
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-- 
Joris Meys
Statistical consultant

Ghent University
Faculty of Bioscience Engineering
Department of Mathematical Modelling, Statistics and Bio-Informatics

tel : +32 9 264 59 87
Joris.Meys at Ugent.be
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[Rd] a^b when a is large and b < 1 (64bit R on windows 7)
Joris Meys