GNU Emacs 21.2.1 (i386-debian-linux-gnu, X toolkit, Xaw3d scroll bars) of 2002-3-22 on raven, modified by Debian

GNU Emacs 21.2.1 (i386-debian-linux-gnu, X toolkit, Xaw3d scroll bars) of 2002-3-22 on raven, modified by Debian

[Mark Barnes]

If I enter this expression in a buffer

(* 85 1.1)

and evaluate it it using Ctrl-x-e, I get the following answer
displayed in the minibuffer:

93.50000000000001

If I evaluate this expression

(- 93.5 (* 85 1.1))

I get this answer in the minibuffer:

-1.4210854715202004e-14

Is this documented in the reference manual?  I was unable to find
anything about this kind of problem.

My Emacs was configured using `configure i386-debian-linux-gnu
--prefix=/usr --sharedstatedir=/var/lib --libexecdir=/usr/lib
--localstatedir=/var/lib --infodir=/usr/share/info
--mandir=/usr/share/man --with-pop=yes --with-x=yes
--with-x-toolkit=athena --without-gif' Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: C
  locale-coding-system: nil
  default-enable-multibyte-characters: t


-- 
Mark R. Barnes, AICP
800 Exchange Street, suite 410
beautiful, sunny, downtown Astoria, OR  97103
voice: 503/325-4356; fax: 503/325-8447
virus-free: Mutt 1.3.28i on Linux 2.4.18

Re: GNU Emacs 21.2.1 (i386-debian-linux-gnu, X toolkit, Xaw3d scroll bars) of 2002-3-22 on raven, modified by Debian

[David Kastrup]

Mark Barnes <mbarnes@pacifier.com> writes:

> If I enter this expression in a buffer
> 
> (* 85 1.1)
> 
> and evaluate it it using Ctrl-x-e, I get the following answer
> displayed in the minibuffer:
> 
> 93.50000000000001
> 
> If I evaluate this expression
> 
> (- 93.5 (* 85 1.1))
> 
> I get this answer in the minibuffer:
> 
> -1.4210854715202004e-14
> 
> Is this documented in the reference manual?  I was unable to find
> anything about this kind of problem.

It is a facet of the well-known fact of life that 10*0.1 hardly ever
is 1.0.

In short: numerics.  0.1 has no exact representation in binary
floating point numbers.


-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum