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Re: sum accuracy

Path csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From Tony van der Hoff <tony@vanderhoff.org>
Newsgroups comp.lang.python
Subject Re: sum accuracy
Date Fri, 15 Apr 2016 11:39:45 +0100
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On 15/04/16 11:10, Ben Bacarisse wrote:
> Oscar Benjamin <oscar.j.benjamin@gmail.com> writes:
>
>> On 15 April 2016 at 10:24, Robin Becker <robin@reportlab.com> wrote:
> <snip>
>>> yes indeed summation is hard :(
>>
>> Not with Fraction it isn't:
>>
>> from fractions import Fraction
>>
>> def exact_sum(nums):
>>      return sum(map(Fraction, nums))
>>
>> This will give you the exact result with precisely zero rounding
>> error. You can convert it to float at the end.
>
> Just a word of warning for people new to numerical work: there's no
> rounding error, but unless you start with Fraction objects you still
> have input or conversion errors.  The uninitiated might expect
>
>    exact_sum([0.3, 0.7])
>
> to be 1.
>

So I'm uninitiated:
NameError: name 'exact_sum' is not defined

I appreciate the word of warning, but, in my case, it's not helpful.

-- 
Tony van der Hoff        | mailto:tony@vanderhoff.org
Buckinghamshire, England |

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Thread

Re: sum accuracy Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2016-04-15 10:36 +0100
  Re: sum accuracy Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-04-15 11:10 +0100
    Re: sum accuracy Tony van der Hoff <tony@vanderhoff.org> - 2016-04-15 11:39 +0100
      Re: sum accuracy Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-04-15 14:31 +0300
    Re: sum accuracy Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-04-15 08:11 -0400
    Re: sum accuracy Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2016-04-15 14:49 +0100
      Re: sum accuracy Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-04-15 17:54 +0100
    Re: sum accuracy Matt Wheeler <m@funkyhat.org> - 2016-04-15 18:04 +0100

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