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Re: should Positive[ complexNumber ] return undefined instead of False?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg112626] Re: should Positive[ complexNumber ] return undefined instead of False?
  • From: Simon <simonjtyler at gmail.com>
  • Date: Thu, 23 Sep 2010 04:23:23 -0400 (EDT)
  • References: <i79ht0$og9$1@smc.vnet.net>

3*I is unmutable. It will always be a non-positive number.
It is also non-negative and not zero, so it's perfectly reasonable
that

In[1]:= {Positive@#,Negative@#,PossibleZeroQ@#}&[3I]
Out[1]= {False,False,False}

Simon

On Sep 21, 4:04 pm, "Nasser M. Abbasi" <n... at 12000.org> wrote:
> math experts:
>
> x = 3*I;
> Positive[x]
>
> Out[59]= False
>
> Should this be undefined or unevaluated?
>
> If it is False, when there must be an case when it is True, right? but
> there is not such case, positive and negative are not defined on the
> complex numbers, or Am I missing something?
>
> I know the above works as documented:
>
> "Positive[x] gives False if x is manifestly a negative numerical
> quantity, a complex numerical quantity, or zero. Otherwise, it remains
> unevaluated"
>
> So, my question is just wanting to know why when Mathematica was
> designed, the complexes were not added to the case where they remains
> unevaluated in this case?
>
> --Nasser



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