From b.rowlingson at lancaster.ac.uk  Wed Feb 13 13:40:48 2008
From: b.rowlingson at lancaster.ac.uk (Barry Rowlingson)
Date: Wed, 13 Feb 2008 12:40:48 +0000
Subject: [Rd] 0.45<0.45 = TRUE (PR#10744)
In-Reply-To: <f8e6ff050802121025w717ef902q7d186d0e1664845f@mail.gmail.com>
References: <1202827999.2701.19.camel@prometheus.geog.ucl.ac.uk>	<XFMail.080212153130.Ted.Harding@manchester.ac.uk>
	<f8e6ff050802121025w717ef902q7d186d0e1664845f@mail.gmail.com>
Message-ID: <47B2E550.2020604@lancaster.ac.uk>

hadley wickham wrote:

> It's more than that as though, as floating point addition is no longer
> guaranteed to be commutative or associative, and multiplication does
> not distribute over addition.  Many concepts that are clear cut in
> pure math become fuzzy in floating point math - equality, singularity
> of matrices etc etc.

  I've just noticed that R doesn't calculate e^pi - pi as equal to 20:

  > exp(pi)-pi == 20
  [1] FALSE

  See: http://www.xkcd.com/217/

Barry



[Rd] 0.45<0.45 = TRUE (PR#10744)
Barry Rowlingson