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Re: Rational[a,b] vs Rational[1,2]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg116640] Re: Rational[a,b] vs Rational[1,2]
  • From: Murray Eisenberg <murray at math.umass.edu>
  • Date: Tue, 22 Feb 2011 04:44:53 -0500 (EST)

I think this sort of thing has been discussed before in this list ad 
nauseam (although usually with respect to things involving I).

On 2/21/2011 7:30 PM, Richard Fateman wrote:
> I find it potentially hazardous that Head[]
> does not distinguish the cases of Head[1/2]
>
> and Head[Rational[a,b]]
>
> Thus these both get transformed...
>
> 1/2  /. Rational[r_,s_]->  foo[r,s]
>
> Rational[a,b] /. Rational[r_,s_] ->  foo[r,s]
>
>
> but compare ...
>
> 1/2  /. 2->4
>
> Rational[a,2] /. 2->4
>
> I'm not saying I'm surprised by this, of course.
>
> Perhaps Rational[a,b] should be converted to a/b unless both
> a and b are numbers.
>
> Oh, for some fun, try Rational[1/2,4].
>
>
> RJF
>
> PS, I used version 7.
>
>

-- 
Murray Eisenberg                     murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower      phone 413 549-1020 (H)
University of Massachusetts                413 545-2859 (W)
710 North Pleasant Street            fax   413 545-1801
Amherst, MA 01003-9305


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