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MathGroup Archive 2005

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Re: Modifying displayed form of an expression?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg57149] Re: Modifying displayed form of an expression?
  • From: "Peltio" <peltio at trilight.zone>
  • Date: Thu, 19 May 2005 03:08:18 -0400 (EDT)
  • References: <d6bi6i$moa$1@smc.vnet.net>
  • Reply-to: "Peltio" <peltioNOSPAM at despammed.com.invalid>
  • Sender: owner-wri-mathgroup at wolfram.com

"AES" wrote

>I have a number of symbolic results which emerge from a Mathematica
>calculation in the form
>
>                a  Exp[b]
>  f  =  ----------------------------------
>              Exp[c] - Exp[d]
>
>where a is "other stuff" and b, c and d are simple sums like b = b1 + b2
>+ b3.  By default Mathematica seems to shuffle the elements of b, c and
>d in these results such that there will be only positive signs in the
>exponents b, c and d.
>
>I want to force Mathematica to display each of these expressions in the
>form
>
>                  a Exp[b - c]
>     -------------------------------------------
>               1 -  Exp[d - c]
>
[snip]
>I've been trying Inputs like
>
>      (Exp[-c] Numerator[f]) / (Exp[-c] Denominator[f])
>
>and not getting anywhere.
>
>Ideas?

How about

    Simplify[Numerator[f] Exp[-c]]/Simplify[Denominator[f] Exp[-c]]

?
It can be streamlined in a simple procedure, like this:

    myCollect[fac_][f_] :=
        Simplify[Numerator[f] fac]/Simplify[Denominator[f] fac]

So that it can be called like this:

    f // myCollect[Exp[-c]]

A further step would be the identification of the positive signed
exponential in the denominator.

cheers,
Peltio




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