Path: csiph.com!usenet.pasdenom.info!aioe.org!news.stack.nl!newsfeed.xs4all.nl!newsfeed1.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail
Return-Path: <rosuav@gmail.com>
X-Original-To: python-list@python.org
Delivered-To: python-list@mail.python.org
X-Spam-Status: OK 0.062
X-Spam-Evidence: '*H*': 0.88; '*S*': 0.00; 'cc:addr:python-list': 0.11; 'coordinates': 0.16; 'from:addr:rosuav': 0.16; 'from:name:chris angelico': 0.16; 'given,': 0.16; 'imo.': 0.16; 'losing': 0.16; 'roy': 0.16; 'wrote:': 0.18; 'trying': 0.19; 'figures': 0.19; 'cc:addr:python.org': 0.22; 'cc:2**0': 0.24; "i've": 0.25; 'values': 0.27; 'header:In-Reply-To:1': 0.27; 'point': 0.28; 'appear': 0.29; 'message-id:@mail.gmail.com': 0.30; "i'm": 0.30; 'but': 0.35; 'received:google.com': 0.35; 'false': 0.36; 'subject:?': 0.36; 'pm,': 0.38; 'then,': 0.60; 'chance': 0.65; 'within': 0.65; 'smith': 0.68; '10%': 0.74; 'gone.': 0.84; 'ten,': 0.84; 'to:none': 0.92
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:cc :content-type; bh=G6ci51i+ap6Ll0O0Wh5+VFcHSawMBlsMUF9RYGrgeLM=; b=fK2f1j5NEINmlAkcp6xyiHrMq0aHaUoMvqvb7b6xMbxvB3sD/z4odUeWA4K84X5ak5 RlMhc6UisDsiAm8AKzz9EM1/5LFxHKM6hNQ4i2vvyTIChE5PIqH7qOHDk7iyB0ZwIJ+y bWdgUb1lqfgv8zsX++aIQ2o+3qVQ26AOmFf+alr/JxjOkkbzjPjYAB3WVCd+jvpzp3LM JAMUwFZK7AQrdF5uYf+zd22HMcr3SNxBV/JtLKZkBA8Slz00mQUfimc+YJIUMNLAhmIf S8eKjWG2lLp1VkPuFFnxb05ST5ixdfUSub/NKS7vVdxrWGJMdVFtmyDVnCjPYqzrVAXp 6Jjg==
MIME-Version: 1.0
X-Received: by 10.52.65.165 with SMTP id y5mr683458vds.51.1398789012216; Tue, 29 Apr 2014 09:30:12 -0700 (PDT)
In-Reply-To: <roy-DA9493.09383329042014@news.panix.com>
References: <mailman.9549.1398700831.18130.python-list@python.org> <535f0f9f$0$29965$c3e8da3$5496439d@news.astraweb.com> <roy-DA9493.09383329042014@news.panix.com>
Date: Wed, 30 Apr 2014 02:30:12 +1000
Subject: Re: Significant digits in a float?
From: Chris Angelico <rosuav@gmail.com>
Cc: "python-list@python.org" <python-list@python.org>
Content-Type: text/plain; charset=UTF-8
X-BeenThere: python-list@python.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: General discussion list for the Python programming language <python-list.python.org>
List-Unsubscribe: <https://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: <https://mail.python.org/mailman/listinfo/python-list>, <mailto:python-list-request@python.org?subject=subscribe>
Newsgroups: comp.lang.python
Message-ID: <mailman.9575.1398789020.18130.python-list@python.org>
Lines: 14
NNTP-Posting-Host: 2001:888:2000:d::a6
X-Trace: 1398789020 news.xs4all.nl 2841 [2001:888:2000:d::a6]:52078
X-Complaints-To: abuse@xs4all.nl
Xref: csiph.com comp.lang.python:70718

On Tue, Apr 29, 2014 at 11:38 PM, Roy Smith <roy@panix.com> wrote:
> I'm trying to intuit, from the values I've been given, which coordinates
> are likely to be accurate to within a few miles.  I'm willing to accept
> a few false negatives.  If the number is float("38"), I'm willing to
> accept that it might actually be float("38.0000"), and I might be
> throwing out a good data point that I don't need to.

You have one chance in ten, repeatably, of losing a digit. That is,
roughly 10% of your four-decimal figures will appear to be
three-decimal, and 1% of them will appear to be two-decimal, and so
on. Is that "a few" false negatives? It feels like a lot IMO. But
then, there's no alternative - the information's already gone.

ChrisA