Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #20790 > unrolled thread

subtraction of floating point numbers

Back to article view | Back to comp.lang.python

Contents

  subtraction of floating point numbers Jaroslav Dobrek <jaroslav.dobrek@gmail.com> - 2012-02-24 00:41 -0800
    Re: subtraction of floating point numbers Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2012-02-24 09:49 +0100
    Re: subtraction of floating point numbers Chris Rebert <clp2@rebertia.com> - 2012-02-24 02:16 -0800

#20790 — subtraction of floating point numbers

Hello,

when I have Python subtract floating point numbers it yields weird
results. Example:

4822.40 - 4785.52 = 36.8799999999992

Why doesn't Python simply yield the correct result? It doesn't have a
problem with this:

482240 - 478552 = 3688

Can I tell Python in some way to do this differently?

Jaroslav

[toc] | [next] | [standalone]

#20792

Jaroslav Dobrek <jaroslav.dobrek@gmail.com> writes:

> when I have Python subtract floating point numbers it yields weird
> results. Example:
>
> 4822.40 - 4785.52 = 36.8799999999992

We've had this discussion here one or two days ago...

The usual answer is: please read "What Every Computer Scientist Should
Know About Floating Point Arithmetic", at:

http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.22.6768

and check the answers posted these last days. In brief: you're working
with floating point numbers, not reals (i.e., real "reals"). That's
life. Deal with it, or move to specialized packages, like decimal.

-- Alain.

[toc] | [prev] | [next] | [standalone]

#20795

On Fri, Feb 24, 2012 at 12:41 AM, Jaroslav Dobrek
<jaroslav.dobrek@gmail.com> wrote:
> Hello,
>
> when I have Python subtract floating point numbers it yields weird
> results. Example:
>
> 4822.40 - 4785.52 = 36.8799999999992
>
> Why doesn't Python simply yield the correct result? It doesn't have a
> problem with this:
>
> 482240 - 478552 = 3688
>
> Can I tell Python in some way to do this differently?

Refer to this thread from 2 days ago:
http://mail.python.org/pipermail/python-list/2012-February/1288344.html

Regards,
Chris

[toc] | [prev] | [standalone]

Back to top | Article view | comp.lang.python

csiph-web