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MathGroup Archive 2005

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Re: Re: Types in Mathematica thread

  • To: mathgroup at smc.vnet.net
  • Subject: [mg62842] Re: [mg62839] Re: Types in Mathematica thread
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Tue, 6 Dec 2005 02:48:32 -0500 (EST)
  • References: <200512060543.AAA03708@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On 6 Dec 2005, at 14:43, Bill Rowe wrote:

> On 12/5/05 at 1:40 PM, akoz at mimuw.edu.pl (Andrzej Kozlowski) wrote:
>
>> On 5 Dec 2005, at 17:37, Kristen W Carlson wrote:
>
>>> I can't think of why there is no RealQ predicate, but there is
>>> _Real, a pattern test via the head.
>
>> Maybe because it is called InexactNumberQ.
>
> That clearly would not be the equivalent of RealQ since  
> InexactNumberQ[Pi] correctly returns False when RealQ[Pi] would  
> return True if it existed.
> --

  The discussion was not about testing whether something is a real  
number or not (in the mathematical sense). This you test with Element 
[something, Reals]. The discussion was about "types". Please note the  
title of the thread to which you have just contributed, or even  
better rerad the thread.  Well, the "type" of objects with head Real  
in Mathematica is exactly what InexactNumberQ tests for. A  
mathematica _Real is not a "real number" in the sense of mathematics  
but precisely an "inexact number".  (Actually, I myself do not agree  
that that there are "types" in Mathematica and that these functions  
test for "types". But even if it were not a discussion of "types" in  
any case your answer would be quite  wrong, since NumberQ[Pi] also  
gives False, and surely Pi is a number?  )

Andrzej Kozlowski


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