Re: python math problem

From	Dennis Lee Bieber <wlfraed@ix.netcom.com>
Subject	Re: python math problem
Date	2013-02-15 17:25 -0500
Organization	> Bestiaria Support Staff <
References	<kfm2t8$9ru$1@ger.gmane.org> <CAPM-O+wEJBOp62m_H9dvp=orS-DxWkuJtBLUc6DMC91aDrv85Q@mail.gmail.com> <kfm5fq$1lr$2@ger.gmane.org>
Newsgroups	comp.lang.python
Message-ID	<mailman.1851.1360967128.2939.python-list@python.org> (permalink)

Show all headers | View raw

On Fri, 15 Feb 2013 15:23:29 -0500, Kene Meniru <Kene.Meniru@illom.org>
declaimed the following in gmane.comp.python.general:

> Joel Goldstick wrote:
> 
> > 
> > This is not a string, it is scientific notion for 1.53... times 10 to the
> > -15th power.  Because of rounding errors caused by doing floating point
> > math on in binary, you get a very small number instead of 0.
> > 
> 
> I was just doing some testing and it was not equating to zero. Perhaps if I 
> rounded it up I may be more successful.

	Classical CompSci teachings when working with floating point numbers
is to NEVER compare for equality. Instead one should compare against
some epsilon:

	if x == y:	#don't do

	if abs(x - y) < epsilon:	#do this

	In your situation, "y" would be 0.0, so the test condenses to

	if abs(x) < epsilon:

and a possible epsilon may be 1.0E-14

-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
        wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

Back to comp.lang.python | Previous | Next — Next in thread | Find similar | Unroll thread

Thread

Re: python math problem Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-02-15 17:25 -0500
  Re: python math problem Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-16 15:49 +1100
    Re: python math problem Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-02-16 13:56 -0500

csiph-web