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MathGroup Archive 1999

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Re: Re: Simplifying constants...bug?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg18613] Re: [mg18559] Re: [mg18489] Simplifying constants...bug?
  • From: "David Park" <djmp at earthlink.net>
  • Date: Tue, 13 Jul 1999 01:01:35 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Alan Calcitti wrote:
>
>here's some intersting behavior in 3.0:
>
>    (a + c*d)/(b + c*d) //. c*d -> -z
>
>gives (as expected):
>
>    (a - z)/(b - z)
>
>yet
>
>    (a + c*d)/(c*d) //. c*d -> -z
>
>no longer simplifes the denominator:
>
>    (a+b-z)/(c*d)
>
>anyone know why?
>
>+------------------------------------------+
>  alan c
>  systems and control engineering
>  case western reserve university
>
>  calvitti at alpha.ces.cwru.edu
>+------------------------------------------+


Because the expressions is actually Times[Power[c, -1], Power[d, -1], Plus[a,
Times[c, d]]]. This works:

(a + c*d)/(c*d) //. { c*d -> -z, 1/(c*d) -> -1/z}

-(a-z)/z

Which brings up the question. Would anybody like to see an alternative output format
which actually shows items in a form which corresponds to FullForm, rational numbers
grouped together, and denominators in the form (1/denominator)? This would certainly
make it easier to "see" the parts of expressions better. It would probably be a great
help to beginners.

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/




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