Groups > comp.lang.python > #20999

Re: Python math is off by .000000000000045

Path	csiph.com!x330-a1.tempe.blueboxinc.net!newsfeed.hal-mli.net!feeder3.hal-mli.net!newsfeed.hal-mli.net!feeder1.hal-mli.net!news.stack.nl!newsfeed.xs4all.nl!newsfeed6.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
Return-Path	<ethan@stoneleaf.us>
X-Original-To	python-list@python.org
Delivered-To	python-list@mail.python.org
X-Spam-Status	OK 0.002
X-Spam-Evidence	'H': 1.00; 'S': 0.00; 'subject:Python': 0.05; 'from:addr:ethan': 0.09; 'from:addr:stoneleaf.us': 0.09; 'from:name:ethan furman': 0.09; 'message-id:@stoneleaf.us': 0.09; 'received:184.172': 0.09; 'received:gator410.hostgator.com': 0.09; '~ethan~': 0.09; 'binary': 0.13; 'hex': 0.16; 'received:72.11': 0.16; 'received:72.11.125': 0.16; 'received:72.11.125.166': 0.16; 'cc:addr:python-list': 0.16; 'wrote:': 0.18; 'cc:no real name:20': 0.21; 'trying': 0.21; "doesn't": 0.22; 'header:In- Reply-To:1': 0.22; 'cc:20': 0.26; 'subject: .': 0.29; 'cc:addr:python.org': 0.29; 'finite': 0.30; "didn't": 0.30; 'quite': 0.31; 'michael': 0.31; 'thanks': 0.32; 'there': 0.33; 'header:User-Agent:1': 0.33; 'showing': 0.34; 'numbers.': 0.34; 'things': 0.35; "he's": 0.37; 'sequence': 0.37; 'doing': 0.38; 'should': 0.38; 'clearly': 0.39; 'that.': 0.39; 'point': 0.40; 'back': 0.60; 'simple': 0.61; 'received:websitewelcome.com': 0.64; 'received:69.93': 0.67
Date	Tue, 28 Feb 2012 09:56:34 -0800
From	Ethan Furman <ethan@stoneleaf.us>
User-Agent	Thunderbird 1.5.0.10 (Windows/20070221)
MIME-Version	1.0
To	Michael Torrie <torriem@gmail.com>
Subject	Re: Python math is off by .000000000000045
References	<mailman.49.1329934400.3037.python-list@python.org> <ji3kb2$hk3$1@reader1.panix.com> <wh92r.13653$1I2.11412@newsfe08.iad> <mailman.162.1330203944.3037.python-list@python.org> <aa5ca147-b5ed-4f8c-935d-48b2c2cfac87@gr6g2000vbb.googlegroups.com> <4f4965f5$0$29989$c3e8da3$5496439d@news.astraweb.com> <cbd3219a-d379-4499-94ea-c4d0178a498f@db5g2000vbb.googlegroups.com> <4F4BBD4C.1050603@stoneleaf.us> <4F4C2595.6030207@gmail.com>
In-Reply-To	<4F4C2595.6030207@gmail.com>
Content-Type	text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding	7bit
X-AntiAbuse	This header was added to track abuse, please include it with any abuse report
X-AntiAbuse	Primary Hostname - gator410.hostgator.com
X-AntiAbuse	Original Domain - python.org
X-AntiAbuse	Originator/Caller UID/GID - [47 12] / [47 12]
X-AntiAbuse	Sender Address Domain - stoneleaf.us
X-BWhitelist	no
X-Source
X-Source-Args
X-Source-Dir
X-Source-Sender	mail.admailinc.com ([192.168.10.136]) [72.11.125.166]:3303
X-Source-Auth	ethan+stoneleaf.us
X-Email-Count	2
X-Source-Cap	dG9idWs7dG9idWs7Z2F0b3I0MTAuaG9zdGdhdG9yLmNvbQ==
Cc	python-list@python.org
X-BeenThere	python-list@python.org
X-Mailman-Version	2.1.12
Precedence	list
List-Id	General discussion list for the Python programming language <python-list.python.org>
List-Unsubscribe	<http://mail.python.org/mailman/options/python-list>, <mailto:python-list-request@python.org?subject=unsubscribe>
List-Archive	<http://mail.python.org/pipermail/python-list>
List-Post	<mailto:python-list@python.org>
List-Help	<mailto:python-list-request@python.org?subject=help>
List-Subscribe	<http://mail.python.org/mailman/listinfo/python-list>, <mailto:python-list-request@python.org?subject=subscribe>
Newsgroups	comp.lang.python
Message-ID	<mailman.255.1330455205.3037.python-list@python.org> (permalink)
Lines	15
NNTP-Posting-Host	2001:888:2000:d::a6
X-Trace	1330455205 news.xs4all.nl 6933 [2001:888:2000:d::a6]:51560
X-Complaints-To	abuse@xs4all.nl
Xref	x330-a1.tempe.blueboxinc.net comp.lang.python:20999

Show key headers only | View raw

Michael Torrie wrote:
> He's simply showing you the hex (binary) representation of the
> floating-point number's binary representation.  As you can clearly see
> in the case of 1.1, there is no finite sequence that can store that.
> You end up with repeating numbers.  

Thanks for the explanation.

> This should help you understand why you get errors
> doing simple things like x/y*y doesn't quite get you back to x.

I already understood that.  I just didn't understand what point he was 
trying to make since he gave no explanation.

~Ethan~

Thread

Python math is off by .000000000000045 Alec Taylor <alec.taylor6@gmail.com> - 2012-02-23 05:13 +1100
  Re: Python math is off by .000000000000045 nn <pruebauno@latinmail.com> - 2012-02-22 10:29 -0800
  Re: Python math is off by .000000000000045 Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2012-02-22 20:44 +0200
  Re: Python math is off by .000000000000045 Grant Edwards <invalid@invalid.invalid> - 2012-02-22 20:48 +0000
    Re: Python math is off by .000000000000045 Tobiah <toby@tobiah.org> - 2012-02-25 09:56 -0800
      Re: Python math is off by .000000000000045 Tim Wintle <tim.wintle@teamrubber.com> - 2012-02-25 19:08 +0000
      Re: Python math is off by .000000000000045 Terry Reedy <tjreedy@udel.edu> - 2012-02-25 16:05 -0500
        Re: Python math is off by .000000000000045 jmfauth <wxjmfauth@gmail.com> - 2012-02-25 13:25 -0800
          Re: Python math is off by .000000000000045 Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-02-25 22:51 +0000
            Re: Python math is off by .000000000000045 jmfauth <wxjmfauth@gmail.com> - 2012-02-26 01:59 -0800
              Re: Python math is off by .000000000000045 Ethan Furman <ethan@stoneleaf.us> - 2012-02-27 09:28 -0800
              Re: Python math is off by .000000000000045 Michael Torrie <torriem@gmail.com> - 2012-02-27 17:53 -0700
              Re: Python math is off by .000000000000045 Ethan Furman <ethan@stoneleaf.us> - 2012-02-28 09:56 -0800
      Re: Python math is off by .000000000000045 Devin Jeanpierre <jeanpierreda@gmail.com> - 2012-02-25 21:49 -0500
      Re: Python math is off by .000000000000045 Terry Reedy <tjreedy@udel.edu> - 2012-02-26 00:44 -0500
  Re: Python math is off by .000000000000045 John Ladasky <ladasky@my-deja.com> - 2012-02-26 16:24 -0800
    Re: Python math is off by .000000000000045 Terry Reedy <tjreedy@udel.edu> - 2012-02-26 20:30 -0500
    Re: Python math is off by .000000000000045 Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-02-27 03:28 +0000
      Re: Python math is off by .000000000000045 Grant Edwards <invalid@invalid.invalid> - 2012-02-27 15:02 +0000
        Re: Python math is off by .000000000000045 Michael Torrie <torriem@gmail.com> - 2012-02-27 08:34 -0700

csiph-web