* (+ 5.1 0.1)
@ 2009-07-13 10:57 leonut
2009-07-13 12:21 ` Anselm Helbig
0 siblings, 1 reply; 4+ messages in thread
From: leonut @ 2009-07-13 10:57 UTC (permalink / raw
To: help-gnu-emacs
First I used "emacs --no-init-file" to start my emacs-22.3, then I
typed (+ 5.1 0.1) in *scratch* buffer. However, when I evaluated this
expression, I got 5.199999999999999.
Can anyone tell me why did this happen?
I tried (+ 5.0 0.1) and (+ 5.2 0.1) and both gave the answers I had
expected.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: (+ 5.1 0.1)
2009-07-13 10:57 (+ 5.1 0.1) leonut
@ 2009-07-13 12:21 ` Anselm Helbig
2009-07-13 12:59 ` Teemu Likonen
0 siblings, 1 reply; 4+ messages in thread
From: Anselm Helbig @ 2009-07-13 12:21 UTC (permalink / raw
To: help-gnu-emacs
Hi!
> First I used "emacs --no-init-file" to start my emacs-22.3, then I
> typed (+ 5.1 0.1) in *scratch* buffer. However, when I evaluated this
> expression, I got 5.199999999999999.
> Can anyone tell me why did this happen?
> I tried (+ 5.0 0.1) and (+ 5.2 0.1) and both gave the answers I had
> expected.
This is a fundamental problem with floating point numbers, something
similar happens in python:
Python 2.5.2 (r252:60911, Jul 31 2008, 17:28:52)
[GCC 4.2.3 (Ubuntu 4.2.3-2ubuntu7)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 5.1 + 0.1
5.1999999999999993
For an explanation why this is so, see e.g. this article:
http://www.theregister.co.uk/2006/08/12/floating_point_approximation/
Or, of course,
http://en.wikipedia.org/wiki/Floating_point#Accuracy_problems
HTH,
Anselm
--
Anselm Helbig
mailto:anselm.helbig+news2009@googlemail.com
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: (+ 5.1 0.1)
2009-07-13 12:21 ` Anselm Helbig
@ 2009-07-13 12:59 ` Teemu Likonen
2009-07-13 13:31 ` leonut
0 siblings, 1 reply; 4+ messages in thread
From: Teemu Likonen @ 2009-07-13 12:59 UTC (permalink / raw
To: help-gnu-emacs
On 2009-07-13 14:21 (+0200), Anselm Helbig wrote:
> This is a fundamental problem with floating point numbers, something
> similar happens in python:
>
> Python 2.5.2 (r252:60911, Jul 31 2008, 17:28:52)
> [GCC 4.2.3 (Ubuntu 4.2.3-2ubuntu7)] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
> >>> 5.1 + 0.1
> 5.1999999999999993
Thanks for info. This is new to me too as I don't know much about
floating point numbers. For that particular example CLISP, a Common Lisp
implementation, gives the correct result:
$ clisp -q -norc -x '(+ 5.1 0.1)'
5.2
Emacs' arbitrary-precision calculator gives 5.2 too:
(calc-eval "5.1 + 0.1")
=> "5.2"
> http://www.theregister.co.uk/2006/08/12/floating_point_approximation/
> http://en.wikipedia.org/wiki/Floating_point#Accuracy_problems
I'll certainly study these.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: (+ 5.1 0.1)
2009-07-13 12:59 ` Teemu Likonen
@ 2009-07-13 13:31 ` leonut
0 siblings, 0 replies; 4+ messages in thread
From: leonut @ 2009-07-13 13:31 UTC (permalink / raw
To: help-gnu-emacs
Thanks very much.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2009-07-13 10:57 (+ 5.1 0.1) leonut
2009-07-13 12:21 ` Anselm Helbig
2009-07-13 12:59 ` Teemu Likonen
2009-07-13 13:31 ` leonut
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