Path: csiph.com!usenet.pasdenom.info!dedibox.gegeweb.org!gegeweb.eu!nntpfeed.proxad.net!proxad.net!feeder1-2.proxad.net!usenet-fr.net!nerim.net!novso.com!newsfeed.xs4all.nl!newsfeed4.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.041 X-Spam-Evidence: '*H*': 0.92; '*S*': 0.00; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; '\xe2\x80\xa6)': 0.09; '*any*': 0.16; 'aiming': 0.16; 'empty,': 0.16; 'expect,': 0.16; 'finney': 0.16; 'losing': 0.16; 'received:80.91.229.3': 0.16; 'received:plane.gmane.org': 0.16; 'roy': 0.16; ':-)': 0.16; 'wrote:': 0.18; 'figures': 0.19; 'header:User-Agent:1': 0.23; 'error': 0.23; 'least': 0.26; 'header:X-Complaints-To:1': 0.27; 'appear': 0.29; 'chris': 0.29; 'kay': 0.31; 'ones.': 0.31; 'writes:': 0.31; 'problem': 0.35; "can't": 0.35; 'good.': 0.35; 'but': 0.35; 'acceptable': 0.36; 'false': 0.36; 'subject:?': 0.36; 'should': 0.36; 'wrong': 0.37; 'so,': 0.37; 'ben': 0.38; 'to:addr :python-list': 0.38; 'to:addr:python.org': 0.39; 'received:org': 0.40; "you're": 0.61; 'high': 0.63; 'different': 0.65; 'chance': 0.65; 'percent': 0.68; 'smith': 0.68; '10%': 0.74; 'article': 0.77; '(10': 0.84; 'glass': 0.84; 'received:125': 0.84; 'ten,': 0.84; 'predictions': 0.91 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Ben Finney Subject: Re: Significant digits in a float? Date: Wed, 30 Apr 2014 10:13:34 +1000 References: <535f0f9f$0$29965$c3e8da3$5496439d@news.astraweb.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Gmane-NNTP-Posting-Host: jigong.madmonks.org X-Public-Key-ID: 0xAC128405 X-Public-Key-Fingerprint: 517C F14B B2F3 98B0 CB35 4855 B8B2 4C06 AC12 8405 X-Public-Key-URL: http://www.benfinney.id.au/contact/bfinney-pubkey.asc X-Post-From: Ben Finney User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.4 (gnu/linux) Cancel-Lock: sha1:5ieU6ah7nNrMFOAcrs8Bk7unh4A= X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Newsgroups: comp.lang.python Message-ID: Lines: 28 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1398816832 news.xs4all.nl 2887 [2001:888:2000:d::a6]:51166 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:70741 Roy Smith writes: > In article , > Chris Angelico wrote: > > > 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? > > You're looking at it the wrong way. It's not that the glass is 10% > empty, it's that it's 90% full, and 90% is a lot of good data :-) The problem is you won't know *which* 90% is accurate, and which 10% is inaccurate. This is very different from the glass, where it's evident which part is good. So, I can't see that you have any choice but to say that *any* of the precision predictions should expect, on average, to be (10 + 1 + …) percent inaccurate. And you can't know which ones. Is that an acceptable error rate? -- \ “If you don't fail at least 90 percent of the time, you're not | `\ aiming high enough.” —Alan Kay | _o__) | Ben Finney