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Re: cannot solve *trivial* equation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg34390] Re: cannot solve *trivial* equation
  • From: Alexander Dreyer <dreyer at itwm.fhg.de>
  • Date: Sat, 18 May 2002 03:50:49 -0400 (EDT)
  • Organization: Fraunhofer ITWM
  • References: <ac2n7c$3qr$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Marco Manfredini wrote:
> 
> Hi,
> 
> I just tried a friend's Mathematica 4.0.0.0:
> 
> Solve[{A == S + Q, Q == 2*S}, A]
> 
> => {A->3*S}
> 
> Solve[{A == S + Q, Q == 2*S}, S]
> 
> => {}
> 
> Can somebody explain this to me? (ie. "bug","you stupid")
> 
> Marco
> 

Hi Marco,
this seems to be a Mathematica bug. If you give "enough" variables to
the Solve command, it is able to solve the system of equations:

In[6]:=
Solve[{A == S + Q, Q == 2*S},{Q, S}]//InputForm

Out[6]//InputForm=
{{Q -> (2*A)/3, S -> A/3}}

Alexander
-- 
 / Alexander Dreyer, Dipl.-Math. - Abteilung Adaptive Systeme        \
/  Fraunhofer Institut fuer Techno- und Wirtschaftsmathematik (ITWM)  \
\  Gottlieb-Daimler-Strasse, Geb. 7^2=49/313  D-67663 Kaiserslautern  /
 \ http://www.itwm.fhg.de    Tel.:(0631)205-2851  Fax:(0631)205-4139 /



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