[Numpy-discussion] making the distinction between -0.0 and 0.0..

[Bruce Southey]

On 09/29/2009 12:08 PM, Gökhan Sever wrote:
>
>
> On Tue, Sep 29, 2009 at 11:53 AM, Christopher Barker 
> <Chris.Barker at noaa.gov <mailto:Chris.Barker at noaa.gov>> wrote:
>
>     Hi folks,
>
>     This isn't really a numpy question, and I'm doing this with
>     regular old
>     python, but I figure you are the folks that would know this:
>
>     How do I get python to make a distinction between -0.0 and 0.0? IN
>     this
>     case, I'm starting with user input, so:
>
>     In [3]: float("-0.0")
>     Out[3]: -0.0
>
>     so python seems to preserve the "-". But:
>
>     In [12]: float("-0.0") == float("0.0")
>     Out[12]: True
>
>     In [13]: float("-0.0") < float("0.0")
>     Out[13]: False
>
>     In [14]: float("0.0") > float("-0.0")
>     Out[14]: False
>
>     It doesn't seem to make the distinction between -0.0 and 0.0 in any of
>     the comparisons. How can I identify -0.0?
>
>     NOTE: numpy behaves the same way, which I think it should, but
>     still...
>
>     My back-up plan is to process the string first, looking for the minus
>     sign, but that will require more changes than I'd like to the rest
>     of my
>     code...
>
>     thanks,
>     -Chris
>
>
>
>     --
>     Christopher Barker, Ph.D.
>     Oceanographer
>
>     Emergency Response Division
>     NOAA/NOS/OR&R            (206) 526-6959   voice
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>
>     Chris.Barker at noaa.gov <mailto:Chris.Barker at noaa.gov>
>     _______________________________________________
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>     NumPy-Discussion at scipy.org <mailto:NumPy-Discussion at scipy.org>
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>
>
> No help from the decimal module. Although its documentation 
> (http://docs.python.org/library/decimal.html) says:
>
> /A decimal number is immutable. It has a sign, coefficient digits, and 
> an exponent. To preserve significance, the coefficient digits do not 
> truncate trailing zeros. Decimals also include special values such as 
> Infinity, -Infinity, and NaN. The standard also differentiates -0 from 
> +0./
>
> When I try:
>
> from decimal import *
> a = Decimal('+0.0')
> b = Decimal('-0.0')
>
> a == b
> True
>
> No help for you either I guess :)
>
> -- 
> Gökhan
> ------------------------------------------------------------------------
>
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>    
Numpy support IEEE floating point standard so you have definitions for 
negative zero (numpy.NZERO) and positive zero (numpy.PZERO):
http://docs.scipy.org/numpy/docs/numpy.NZERO/
http://docs.scipy.org/numpy/docs/numpy.PZERO/

Bruce


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