Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail From: Random832 Newsgroups: comp.lang.python Subject: Re: sum accuracy Date: Wed, 13 Apr 2016 13:05:10 -0400 Lines: 16 Message-ID: References: <570E78F9.8050409@chamonix.reportlab.co.uk> <1460567110.3933817.577783969.165F6097@webmail.messagingengine.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit X-Trace: news.uni-berlin.de kn0zQb7CxKc9RQnHQQTjZASTY3MMIe1HV+ApnJvx8JfQ== Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.016 X-Spam-Evidence: '*H*': 0.97; '*S*': 0.00; 'operator': 0.03; '(except': 0.05; 'received:internal': 0.09; 'wed,': 0.15; 'assumptions': 0.16; 'message-id:@webmail.messagingengine.com': 0.16; 'received:10.202': 0.16; 'received:10.202.2': 0.16; 'received:66.111': 0.16; 'received:66.111.4': 0.16; 'received:io': 0.16; 'received:messagingengine.com': 0.16; 'received:psf.io': 0.16; 'semantically': 0.16; 'wrote:': 0.16; "wouldn't": 0.16; 'tests': 0.18; 'algorithm': 0.20; 'header:In-Reply-To:1': 0.24; 'example': 0.26; 'equivalent': 0.27; '13,': 0.29; 'types.': 0.29; 'url:activestate': 0.29; 'anyone': 0.32; "can't": 0.32; 'point': 0.33; 'url:code': 0.34; 'that,': 0.34; 'but': 0.36; 'to:addr :python-list': 0.36; 'subject:: ': 0.37; 'received:10': 0.37; 'seem': 0.37; 'no,': 0.38; 'received:66': 0.38; 'anything': 0.38; 'does': 0.39; 'to:addr:python.org': 0.40; 'header:Message-Id:1': 0.61; 'show': 0.62; 'real': 0.62; 'more': 0.63; 'sum': 0.69; 'special': 0.73; 'algorithm,': 0.84; 'becker': 0.84; 'strings),': 0.84; 'url:recipes': 0.84 DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; d=fastmail.com; h= content-transfer-encoding:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to:x-sasl-enc :x-sasl-enc; s=mesmtp; bh=lArsGJtF0PoedbWPuhua2moDfLg=; b=bzxmwf fbyZmYQy28L047DnUUHSM8zGYDbrpeoNQoeRUDVMjbrWYPtncPqcdSClyQi9qd9h PD1+urTKq5iGZFTXVIQZ6Yyvp/GvikhYZ7exTZRWJjC8pAaluhyXytqnO3NZsEWN 9fFuTmSL4sflGuQzf9Gxr6GMvId4CnGI2L11g= DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; d= messagingengine.com; h=content-transfer-encoding:content-type :date:from:in-reply-to:message-id:mime-version:references :subject:to:x-sasl-enc:x-sasl-enc; s=smtpout; bh=lArsGJtF0PoedbW Puhua2moDfLg=; b=Agy+Uq83chBIq5ehcAtzL6f9ahXg8Rri/D7uGOLLmJlen3M kK6g4IKeWUEhLDY7Dcb3INk6pYmKfFoL4rBrjt+l+tYhOBZ5bB37gJI847NsVCTr DDIVVo9GrExmxustKvxpJsDU/fVHZiQBnS0ZImEddrDA6iOue8zl586Mf0lk= X-Sasl-Enc: gq7ehRqlk6Y/oOsKUD0cyMpv5ODcL2yD01bnKBAuVZ9c 1460567110 X-Mailer: MessagingEngine.com Webmail Interface - ajax-7bc02efc In-Reply-To: <570E78F9.8050409@chamonix.reportlab.co.uk> X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Mailman-Original-Message-ID: <1460567110.3933817.577783969.165F6097@webmail.messagingengine.com> X-Mailman-Original-References: <570E78F9.8050409@chamonix.reportlab.co.uk> Xref: csiph.com comp.lang.python:106961 On Wed, Apr 13, 2016, at 12:51, Robin Becker wrote: > Does anyone know if sum does anything special to try and improve > accuracy? My > simple tests seem to show it is exactly equivalent to a for loop > summation. No, it doesn't. Sum works on any type that can be added (except strings), it can't make any assumptions about the characteristics of floating point types. For non-numeric types, the addition operator may not be semantically commutative or associative. Look at http://code.activestate.com/recipes/393090-binary-floating-point-summation-accurate-to-full-p/ for an example of a more accurate algorithm, but note that, for example, this algorithm wouldn't work on complex numbers (you'd have to sum the real and imaginary components separately)