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RE: cannot solve *trivial* equation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg34394] RE: [mg34380] cannot solve *trivial* equation
  • From: "Florian Jaccard" <jaccardf at eicn.ch>
  • Date: Sat, 18 May 2002 03:50:54 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

It is good like that !

(N.B : Don't use capital letters ! A lot of them are already used by the
programm...)

In fact, if you want to solve for s,
you must have simultaneously  s = (1/2)q and s = (1/3)a !
Mathematica can't make such assumptions !

But what you wanted to do is "discuss" the system.

For this purpose, use "Reduce" :

In[29]:= Reduce[{a == s + q,q == 2*s},s]

Out[29]= 2a == 3q && s == q/2

(&& is the logical "and" , || the logical "or")

Meilleures salutations

Florian Jaccard
EICN-HES
e-mail : jaccardf at eicn.ch


-----Message d'origine-----
De : Marco Manfredini [mailto:marco at technoboredom.net]
Envoyé : ven., 17. mai 2002 12:31
À : mathgroup at smc.vnet.net
Objet : [mg34380] cannot solve *trivial* equation


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







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