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To: python-list@python.org
From: Dennis Lee Bieber <wlfraed@ix.netcom.com>
Subject: Re: python math problem
Date: Fri, 15 Feb 2013 17:25:20 -0500
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Xref: csiph.com comp.lang.python:38964

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/