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MathGroup Archive 2007

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Re: [TS 48]--Re:why isn't Rational[1,2] (apparently) atomic until it is evaluated?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg72540] Re: [TS 48]--Re:why isn't Rational[1,2] (apparently) atomic until it is evaluated?
  • From: "Chris Chiasson" <chris at chiasson.name>
  • Date: Fri, 5 Jan 2007 02:34:17 -0500 (EST)
  • References: <200701041530.l04FU7BT023687@localhost.localdomain>

You are right that unevaluated Rational expressions are not Atomic.
However, I was wondering why... ?

On Thu, 4 Jan 2007 15:30:07 UT, mathgroup <mathgroup at smc.vnet.net> wrote:
>  -- Wolfram Research Technical Support --
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> Our classification number for this message is: [TS 48]
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> From: "Chris Chiasson" <chris at chiasson.name>
> Date: Tue, 2 Jan 2007 02:04:41 -0600
> Subject: why isn't Rational[1,2] (apparently) atomic until it is evaluated?
> To: mathgroup <mathgroup at smc.vnet.net>,"support at wolfram.com" <support at wolfram.com>
>
> {Map[Hold,Rational[1,2],{0}],
>     Hold[Rational[1,2]]}/.x_?NumberQ/;((Print[FullForm@x," ",#];#)&)@
>         AtomQ@Unevaluated@x\[RuleDelayed]SetPrecision[x,MachinePrecision]
>
> gives:
>
> From In[39]:=
> Rational[1,2] True
>
> From In[39]:=
> Rational[1,2] False
>
> From In[39]:=
> 1 True
>
> From In[39]:=
> 2 True
>
> Out[39]=
> {Hold[SetPrecision[1/2, MachinePrecision]],
> Hold[Rational[SetPrecision[1, MachinePrecision],
>     SetPrecision[2, MachinePrecision]]]}
>
> --
> http://chris.chiasson.name/
>
>
>
>
> ___________________________________________________________________________
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Chris,
>
> I suspect that I may be missing something here.
>
> Given that:
>
> AtomQ[expr] yields True if expr is an expression which cannot be divided into \
> subexpressions, and yields False otherwise
>
> It seems that unevaluated Rational expressions would not be atomic.
>
> Let me know is there is another way to look at it.
>
> Tom Zeller
> Wolfram Research Technical Support - Student Versions
>
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-- 
http://chris.chiasson.name/


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