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Re: Solve[] doesn't

  • To: mathgroup at smc.vnet.net
  • Subject: [mg90631] Re: Solve[] doesn't
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Thu, 17 Jul 2008 05:33:30 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <g5kil1$8lf$1@smc.vnet.net>

Hauke Reddmann wrote:

> This is extremely annoying.     
> I have a very large (this seems to be critical) equation
> system. It's partly linear, partly horror, but already
> after I solve the linear part, a certain solution (which
> is obviously one since substituting it in makes all equations
> identical zero) can't be found anymore. The solution has some
> surds (this also seems critical, the ones without are found) 
> but the equations are strictly polynomic.
> 
> Faked Example (the real one only PM-ed, since it's a bit
> oversized):
> 
> x-y=1
> x^2+y^2=3
> x^3-y^3=4
> and after y was eliminated, it doesn't find x. (=golden mean here)
>   
> Huh?

Hum, I might not have understood correctly your problem really is, but 
my interpretation of your example works fine on my system (i.e. Solve[] 
returns the correct values for y *and* x):

     In[1]:= sys = {x - y == 1, x^2 + y^2 == 3, x^3 - y^3 == 4};
     sols = Solve[sys]
     sys /. sols

     Out[2]=
            1                     1
     {{x -> - (1 - Sqrt[5]), y -> - (-1 - Sqrt[5])},
            2                     2

             1                     1
       {x -> - (1 + Sqrt[5]), y -> - (-1 + Sqrt[5])}}
             2                     2

     Out[3]= {{True, True, True}, {True, True, True}}

     In[4]:= $Version

     Out[4]= 6.0 for Mac OS X x86 (64-bit) (May 21, 2008)


Regards,
-- Jean-Marc


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