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MathGroup Archive 2004

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Re: Re: Reduce/Solve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg49995] Re: [mg49990] Re: Reduce/Solve
  • From: DrBob <drbob at bigfoot.com>
  • Date: Tue, 10 Aug 2004 06:02:51 -0400 (EDT)
  • References: <200408090829.EAA03580@smc.vnet.net>
  • Reply-to: drbob at bigfoot.com
  • Sender: owner-wri-mathgroup at wolfram.com

It's especially sad, coming on the heels of Andrsej's valiant DEFENSE of Reduce!

Bobby

On Mon, 9 Aug 2004 04:29:32 -0400 (EDT), Dana DeLouis <delouis at bellsouth.net> wrote:

> Hello.  It is because of Mathematica's huge bug in variable names.  Reduce
> often doesn't work because of this bug.  The first thing you need to try is
> to change the variable name.  I would first start by changing the "r" to a
> variable name that comes near the beginning of the alphabet, like "a" (at
> least something before the "d" in the equation).
>
> Taking your equation, and changing r to a:
>
> eq = J == J0*(1 + r/d)*Exp[-(r/d)] /. r -> a
>
> J == ((1 + a/d)*J0)/E^(a/d)
>
> Now it should work:
>
> tt = Reduce[eq, a]
>
> d != 0 && J == 0 &&
>    (J0 == 0 || a == -d) ||
>   C[1] ? Integers &&
>    J != 0 && J0 != 0 &&
>    d != 0 && a ==
>     -d - d*ProductLog[C[1],
>        -(J/(E*J0))]
>
> HTH
> Sad, isn't it!
>
> Dana
>
>
> "Dr A.H. Harker" <a.harker at ucl.ac.uk> wrote in message
> news:cetf3i$6i8$1 at smc.vnet.net...
>> Dear All,
>>          I tend to think of Reduce as a more powerful tool than Solve,
>> yet with
>>
>> eq = J == J0 (1 + r/d) Exp[-r/d]
>> ss = Solve[eq, r]
>> tt = Reduce[eq, r]
>>
>>  I get useful output from Solve, but Reduce returns the expression
>> unevaluated. What am I missing?  Mathematica 5.0.0.0 under Windows XP.
>>
>>        Tony
>>
>>  Dr A.H. Harker
>>  Director of Postgraduate Studies
>>  Deputy Head, Condensed Matter and Materials Physics Group
>>  Department of Physics and Astronomy
>>  University College London
>>  Gower Street
>>  LONDON
>>  WC1E  6BT
>>  (44)(0)207 679 3404
>>  a.harker at ucl.ac.uk
>>
>>
>>
>
>
>



-- 
DrBob at bigfoot.com
www.eclecticdreams.net


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