Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!eternal-september.org!feeder.eternal-september.org!feeds.phibee-telecom.net!newsfeed.xs4all.nl!newsfeed5.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 0.007 X-Spam-Evidence: '*H*': 0.99; '*S*': 0.00; '64-bit': 0.07; 'python': 0.09; 'accuracy.': 0.09; 'options.': 0.15; '3.3,': 0.16; 'accuracy,': 0.16; 'from:addr:rosuav': 0.16; 'from:name:chris angelico': 0.16; 'losing': 0.16; 'outputs': 0.16; 'skip:( 90': 0.16; 'skip:7 20': 0.16; 'tying': 0.16; 'wrote:': 0.17; '>>>': 0.18; 'import': 0.21; 'received:209.85.214.174': 0.21; 'fraction': 0.22; 'subject:problem': 0.22; 'script': 0.24; 'header:In-Reply- To:1': 0.25; 'am,': 0.27; 'separate': 0.27; 'question': 0.27; 'message-id:@mail.gmail.com': 0.27; 'run': 0.28; 'decimal': 0.29; 'probably': 0.29; 'fri,': 0.30; 'skip:( 40': 0.30; 'switch': 0.32; 'to:addr:python-list': 0.33; 'point.': 0.33; 'that,': 0.34; 'received:google.com': 0.34; 'acceptable': 0.35; 'nov': 0.35; 'received:209.85': 0.35; 'there': 0.35; 'but': 0.36; 'should': 0.36; 'too': 0.36; 'possible': 0.37; 'two': 0.37; 'ones': 0.37; 'received:209': 0.37; 'subject:: ': 0.38; 'to:addr:python.org': 0.39; 'received:209.85.214': 0.39; 'build': 0.39; 'header:Received:5': 0.40; 'your': 0.60; 'different': 0.63; 'more': 0.63; 'lose': 0.71; 'increase': 0.72 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:to :content-type; bh=0WItBQm8g+KC/pqrn6oIH8BYsHks036Dr3/RPsidzkM=; b=TxJBeAzfiiIJUX5CBFRxFgNAJPe7+AyIOcEqA4UufGhW9AgF5dpoF2RsSo9c2/SnPe dJxVEHqg4jKcZZEpN1s3oovdwJFzYMx/8i1tnJTcMb36W55tFC8Y5HapEaFtMyzz+5mL v7u5ygqV8s/grNm0FQeHRm8r8hZp1RFawBpL073uHbJcdzbtiGoQ5OeLPps6mv+fbJ2e UCjimN+0LLpWd3t7/VuPzYkBH5jh+Z4uNxAvG4hpFmsy/eRX6GKsJDa9SbWmD1N1MgfF dVYTlXYvYkuq+IHOitYJvCET7XKbr/HSqVG2hkjd/pGz0kusQu/V2uAbKoZQNBfFV7Dh yLNQ== MIME-Version: 1.0 In-Reply-To: References: Date: Fri, 9 Nov 2012 04:13:33 +1100 Subject: Re: accuracy problem in calculation From: Chris Angelico To: python-list@python.org Content-Type: text/plain; charset=ISO-8859-1 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: 32 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1352394817 news.xs4all.nl 6917 [2001:888:2000:d::a6]:32925 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:32964 On Fri, Nov 9, 2012 at 4:05 AM, Debashish Saha wrote: > (1500000000+1.00067968)-(1500000000+1.00067961) > Out[102]: 2.384185791015625e-07 > > 1.00067968-(1.00067961) > Out[103]: 7.000000001866624e-08 > > above i am showing the two different results,though the two outputs > should be same if we do it in copy(the lass one is acceptable value). > so my question is how to increase the accuracy(windows7(32bit) > ,python2.7.2) Welcome to floating point. You're working with very large and very small numbers, and you _will_ lose accuracy. There are a few options. It's possible that a 64-bit build of Python will give you more accuracy, but better would be to separate your huge numbers from your tiny ones and work with them separately. Alternatively, switch to the Decimal or Fraction types, but be aware that your script will probably run a lot slower. >>> from decimal import Decimal >>> (Decimal("1500000000")+Decimal("1.00067968"))-(Decimal("1500000000")+Decimal("1.00067961")) Decimal('7E-8') >>> Decimal("1.00067968")-Decimal("1.00067961") Decimal('7E-8') Unless something's tying you to Python 2, consider moving to Python 3. You may find that, on Python 3.3, you can switch to Decimal without losing too much performance. ChrisA