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What is precision of a number representation? (was: Curious Omission In New-Style Formats)

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From Ben Finney <ben+python@benfinney.id.au>
Newsgroups comp.lang.python
Subject What is precision of a number representation? (was: Curious Omission In New-Style Formats)
Date Tue, 12 Jul 2016 06:56:10 +1000
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Ethan Furman <ethan@stoneleaf.us> writes:

> I will readily admit to not having a maths degree, and so of course to
> me saying the integer 123 has a precision of 5, 10, or 99 digits seems
> like hogwash to me.

Precision is not a property of the number. It is a property of the
*representation* of that number.

The representation “1×10²” has a precision of one digit.
The representation “100” has a precision of three digits.
The representation “00100” has a precision of five digits.
The representation “100.00” also has a precision of five digits.

Those can all represent the same number; or maybe some of them represent
“one hundred” and others represent “one hundred and a millionth”.

The representation is only an approximation of the actual number, and
the precision tells us how fuzzy the approximation is.

None of these say how *accurate* the representation is; if those are
representations of the number “seven thousand” they are not very
accurate, while they might be passably accurate for the number “one
hundred and seventy”.

> But I'm always willing to learn.  So please explain what 123 with a
> precision of five integer digits means, and what to do we gain by
> saying such a thing?

We gain clarity of speech: we distinguish the different aspects (how
many digits of this representation are actually claimed to represent the
number?) communicated by a representation.

-- 
 \        “… no testimony can be admitted which is contrary to reason; |
  `\   reason is founded on the evidence of our senses.” —Percy Bysshe |
_o__)                        Shelley, _The Necessity of Atheism_, 1811 |
Ben Finney

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Curious Omission In New-Style Formats Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-07-09 22:54 -0700
  Re: Curious Omission In New-Style Formats Ian Kelly <ian.g.kelly@gmail.com> - 2016-07-10 01:21 -0600
    Re: Curious Omission In New-Style Formats Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-07-10 17:34 -0700
      Re: Curious Omission In New-Style Formats Ian Kelly <ian.g.kelly@gmail.com> - 2016-07-11 09:04 -0600
        Re: Curious Omission In New-Style Formats Steven D'Aprano <steve@pearwood.info> - 2016-07-12 02:28 +1000
          Re: Curious Omission In New-Style Formats Ethan Furman <ethan@stoneleaf.us> - 2016-07-11 10:24 -0700
            Re: Curious Omission In New-Style Formats Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-07-12 11:47 +1200
              Re: Curious Omission In New-Style Formats Ethan Furman <ethan@stoneleaf.us> - 2016-07-11 17:24 -0700
              Re: Curious Omission In New-Style Formats Ian Kelly <ian.g.kelly@gmail.com> - 2016-07-11 19:16 -0600
          Re: Curious Omission In New-Style Formats Ian Kelly <ian.g.kelly@gmail.com> - 2016-07-11 12:38 -0600
            Re: Curious Omission In New-Style Formats Steven D'Aprano <steve@pearwood.info> - 2016-07-12 13:38 +1000
              Re: Curious Omission In New-Style Formats Ian Kelly <ian.g.kelly@gmail.com> - 2016-07-13 00:21 -0600
                Re: Curious Omission In New-Style Formats Marko Rauhamaa <marko@pacujo.net> - 2016-07-13 09:57 +0300
                Re: Curious Omission In New-Style Formats Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-07-13 00:05 -0700
                Re: Curious Omission In New-Style Formats Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-07-13 18:49 +1000
                Re: Curious Omission In New-Style Formats Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2016-07-13 16:01 +0200
                Re: Curious Omission In New-Style Formats Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-07-13 20:04 -0400
                Re: Curious Omission In New-Style Formats Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-07-13 15:24 -0700
                Re: Curious Omission In New-Style Formats Ian Kelly <ian.g.kelly@gmail.com> - 2016-07-13 18:45 -0600
                Re: Curious Omission In New-Style Formats Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-07-13 20:39 -0700
                Re: Curious Omission In New-Style Formats Ian Kelly <ian.g.kelly@gmail.com> - 2016-07-13 23:18 -0600
                Re: Curious Omission In New-Style Formats Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-07-14 17:47 +1000
                Re: Curious Omission In New-Style Formats Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-07-14 07:34 -0400
                Re: Curious Omission In New-Style Formats Ian Kelly <ian.g.kelly@gmail.com> - 2016-07-14 08:30 -0600
                Re: Curious Omission In New-Style Formats Marko Rauhamaa <marko@pacujo.net> - 2016-07-14 19:02 +0300
                Re: Curious Omission In New-Style Formats Ian Kelly <ian.g.kelly@gmail.com> - 2016-07-14 11:10 -0600
                Re: Curious Omission In New-Style Formats Marko Rauhamaa <marko@pacujo.net> - 2016-07-14 20:30 +0300
                Re: Curious Omission In New-Style Formats Ian Kelly <ian.g.kelly@gmail.com> - 2016-07-14 18:17 -0600
                Re: Curious Omission In New-Style Formats Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-07-14 18:08 -0700
                Re: Curious Omission In New-Style Formats Marko Rauhamaa <marko@pacujo.net> - 2016-07-15 09:06 +0300
                Re: Curious Omission In New-Style Formats Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2016-07-15 09:54 +0200
                Re: Curious Omission In New-Style Formats Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-07-15 11:40 +0300
                Re: Curious Omission In New-Style Formats Steven D'Aprano <steve@pearwood.info> - 2016-07-15 20:56 +1000
                Re: Curious Omission In New-Style Formats Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2016-07-15 13:44 +0200
                Re: Curious Omission In New-Style Formats Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-07-15 16:38 +0300
                Re: Curious Omission In New-Style Formats Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2016-07-15 16:47 +0200
                Re: Curious Omission In New-Style Formats Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-07-15 16:13 +0300
                Re: Curious Omission In New-Style Formats Steven D'Aprano <steve@pearwood.info> - 2016-07-16 01:12 +1000
                Re: Curious Omission In New-Style Formats Random832 <random832@fastmail.com> - 2016-07-15 09:39 -0400
                Re: Curious Omission In New-Style Formats Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2016-07-15 16:32 +0200
                Re: Curious Omission In New-Style Formats Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2016-07-15 13:05 +0200
                Re: Curious Omission In New-Style Formats Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-07-15 16:28 +0300
                Re: Curious Omission In New-Style Formats Steven D'Aprano <steve@pearwood.info> - 2016-07-16 01:13 +1000
                Re: Curious Omission In New-Style Formats Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-07-15 18:27 +0300
                Re: Curious Omission In New-Style Formats Marko Rauhamaa <marko@pacujo.net> - 2016-07-15 12:20 +0300
                Re: Curious Omission In New-Style Formats Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2016-07-15 12:44 +0200
                Re: Curious Omission In New-Style Formats Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-07-14 16:26 -0700
                Re: Curious Omission In New-Style Formats Robert Kern <robert.kern@gmail.com> - 2016-07-14 16:17 +0100
                Re: Curious Omission In New-Style Formats Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-07-15 16:35 -0700
                Re: Curious Omission In New-Style Formats Chris Angelico <rosuav@gmail.com> - 2016-07-16 10:57 +1000
                Re: Curious Omission In New-Style Formats MRAB <python@mrabarnett.plus.com> - 2016-07-14 01:59 +0100
              Re: Curious Omission In New-Style Formats Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-07-13 07:46 -0400
                Re: Curious Omission In New-Style Formats Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-07-13 16:04 +0300
              Re: Curious Omission In New-Style Formats Chris Angelico <rosuav@gmail.com> - 2016-07-13 23:00 +1000
                Re: Curious Omission In New-Style Formats Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-07-13 16:16 +0300
                Re: Curious Omission In New-Style Formats Chris Angelico <rosuav@gmail.com> - 2016-07-13 23:49 +1000
                Re: Curious Omission In New-Style Formats Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-07-13 17:23 +0300
                Re: Curious Omission In New-Style Formats Chris Angelico <rosuav@gmail.com> - 2016-07-14 00:28 +1000
          Re: Curious Omission In New-Style Formats Terry Reedy <tjreedy@udel.edu> - 2016-07-11 14:54 -0400
          Re: Curious Omission In New-Style Formats Ian Kelly <ian.g.kelly@gmail.com> - 2016-07-11 13:27 -0600
          Re: Curious Omission In New-Style Formats Michael Torrie <torriem@gmail.com> - 2016-07-11 14:06 -0600
          Re: Curious Omission In New-Style Formats Random832 <random832@fastmail.com> - 2016-07-11 16:34 -0400
          Re: Curious Omission In New-Style Formats Terry Reedy <tjreedy@udel.edu> - 2016-07-11 16:52 -0400
          What is precision of a number representation? (was: Curious Omission In New-Style Formats) Ben Finney <ben+python@benfinney.id.au> - 2016-07-12 06:56 +1000
            Re: What is precision of a number representation? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-07-11 23:28 +0100
          Re: What is precision of a number representation? Ethan Furman <ethan@stoneleaf.us> - 2016-07-11 14:22 -0700
          Re: What is precision of a number representation? (was: Curious Omission In New-Style Formats) Chris Angelico <rosuav@gmail.com> - 2016-07-12 07:51 +1000
            Re: What is precision of a number representation? (was: Curious Omission In New-Style Formats) Jan Coombs <jenfhaomndgfwutc@murmic.plus.com> - 2016-07-12 00:14 +0100
              Re: What is precision of a number representation? (was: Curious Omission In New-Style Formats) Chris Angelico <rosuav@gmail.com> - 2016-07-12 09:57 +1000
            Re: What is precision of a number representation? (was: Curious Omission In New-Style Formats) Steven D'Aprano <steve@pearwood.info> - 2016-07-12 14:19 +1000
              Re: What is precision of a number representation? (was: Curious Omission In New-Style Formats) Chris Angelico <rosuav@gmail.com> - 2016-07-12 14:36 +1000
              Re: What is precision of a number representation? Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2016-07-12 11:50 +0200
                Re: What is precision of a number representation? Marko Rauhamaa <marko@pacujo.net> - 2016-07-12 13:27 +0300
                Re: What is precision of a number representation? Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2016-07-12 13:02 +0200
                Re: What is precision of a number representation? Steven D'Aprano <steve@pearwood.info> - 2016-07-12 23:16 +1000
          Re: What is precision of a number representation? Ethan Furman <ethan@stoneleaf.us> - 2016-07-11 15:17 -0700
            Re: What is precision of a number representation? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-07-12 16:21 +1000
              Re: What is precision of a number representation? Random832 <random832@fastmail.com> - 2016-07-12 09:36 -0400
          Re: What is precision of a number representation? Ethan Furman <ethan@stoneleaf.us> - 2016-07-11 15:29 -0700
          Re: Curious Omission In New-Style Formats Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-07-12 11:26 +1200
          Re: What is precision of a number representation? Chris Angelico <rosuav@gmail.com> - 2016-07-12 11:57 +1000
          Re: What is precision of a number representation? Ben Finney <ben+python@benfinney.id.au> - 2016-07-12 13:41 +1000
          Re: What is precision of a number representation? Terry Reedy <tjreedy@udel.edu> - 2016-07-12 00:14 -0400
          Re: What is precision of a number representation? Terry Reedy <tjreedy@udel.edu> - 2016-07-12 00:17 -0400

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