Path: csiph.com!usenet.pasdenom.info!news.redatomik.org!newsfeed.xs4all.nl!newsfeed2.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 0.008 X-Spam-Evidence: '*H*': 0.98; '*S*': 0.00; 'else:': 0.03; 'elif': 0.04; 'root': 0.04; '"""': 0.05; 'attributes': 0.07; 'received:67.192': 0.09; 'received:67.192.241': 0.09; 'received:dfw.emailsrvr.com': 0.09; 'underlying': 0.09; 'python': 0.11; 'def': 0.14; 'b):': 0.16; 'subject:distance': 0.16; 'such,': 0.16; 'thoughts?': 0.16; 'wrote:': 0.16; 'alternate': 0.18; 'python?': 0.18; 'received:emailsrvr.com': 0.22; 'comment:': 0.23; "i've": 0.24; 'header:In-Reply-To:1': 0.24; 'header:User-Agent:1': 0.26; 'objects': 0.29; 'received:(smtp server)': 0.31; 'point': 0.33; 'another': 0.34; 'to:addr:python-list': 0.35; 'handle': 0.36; 'statement': 0.36; 'should': 0.37; 'subject:: ': 0.37; 'pm,': 0.39; 'does': 0.39; 'to:addr:python.org': 0.39; 'received:192': 0.39; 'where': 0.40; 'your': 0.60; 'subject:more': 0.61; 'more': 0.62; 'distance': 0.63; 'course': 0.64; 'between': 0.65; 'charset:windows-1252': 0.65; 'matter.': 0.66; 'special': 0.72; 'lose': 0.76; 'square': 0.76; 'discovered': 0.83; 'calculations': 0.84; 'herron': 0.84; 'suffer': 0.93 X-Sender-Id: gary.herron@islandtraining.com Date: Mon, 25 May 2015 13:20:07 -0700 From: Gary Herron User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: python-list@python.org Subject: Re: a more precise distance algorithm References: In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.20+ 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: 39 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1432585603 news.xs4all.nl 2854 [2001:888:2000:d::a6]:43585 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:91212 On 05/25/2015 12:21 PM, ravas wrote: > I read an interesting comment: > """ > The coolest thing I've ever discovered about Pythagorean's Theorem is an alternate way to calculate it. If you write a program that uses the distance form c = sqrt(a^2 + b^2) you will suffer from the lose of half of your available precision because the square root operation is last. A more accurate calculation is c = a * sqrt(1 + b^2 / a^2). If a is less than b, you should swap them and of course handle the special case of a = 0. > """ > > Is this valid? > Does it apply to python? This is a statement about floating point numeric calculations on a computer,. As such, it does apply to Python which uses the underlying hardware for floating point calculations. Validity is another matter. Where did you find the quote? Gary Herron > Any other thoughts? :D > > My imagining: > > def distance(A, B): > """ > A & B are objects with x and y attributes > :return: the distance between A and B > """ > dx = B.x - A.x > dy = B.y - A.y > a = min(dx, dy) > b = max(dx, dy) > if a == 0: > return b > elif b == 0: > return a > else: > return a * sqrt(1 + (b / a)**2)