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MathGroup Archive 2005

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Re: Solve with assumptions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg57808] Re: Solve with assumptions
  • From: dh <dh at metrohm.ch>
  • Date: Thu, 9 Jun 2005 05:17:41 -0400 (EDT)
  • References: <d86937$c7n$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi Muktar,
try e.g. Reduce. Here is a small example.

Reduce[{x^3 + 1 == 0}, x] gives
x == -1 || x == (-1)^(1/3) || x == -(-1)^(2/3)
on real and two complex solutions.
However:
Reduce[{Element[x, Reals], x^3 + 1 == 0}, x]
gives
x == -1
or another example: Reduce[{x < 0, x^2 - 1 == 0}, x]

sincerely, Daniel

Mukhtar Bekkali wrote:
> I need to solve equation f[x1,x2] for x1 and x2, where I know that x1>0
> and x2>0 and are both real.  Solve[f[x1,x2]==0,{x1,x2}] takes a lot of
> time to solve and when it does solve it gives me tons of unreal
> solutions or repetitive solutions (I have enabled Miscellanous RealOnly
> and instead of complex solutions it just gives me Unreal).  I would
> like to know how I (1) can restrict the solution set where Mathematica
> is trying to find a solution, and (2) show only unique solutions and
> totally not showing Unreal ones. FindRoot is great but it is very
> dependent on starting values which is not good for me. Thankx, Mukhtar
> Bekkali
> 


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