Re: Reduce/Solve

• To: mathgroup at smc.vnet.net
• Subject: [mg49990] Re: Reduce/Solve
• From: "Dana DeLouis" <delouis at bellsouth.net>
• Date: Mon, 9 Aug 2004 04:29:32 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```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

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
>  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
>
>
>

```

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