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Re: Find a single solution to a system of equations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg121852] Re: Find a single solution to a system of equations
  • From: Peter Pein <petsie at dordos.net>
  • Date: Wed, 5 Oct 2011 03:59:51 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <j6e648$kd6$1@smc.vnet.net>

Am 04.10.2011 07:38, schrieb jamievicary at NgOmSaPiAlM.com:
> Hi,
>
> I have a system of equations, and want to use Mathematica to find a
> single solution. It's no good using Solve, because then Mathematica
> tries to find all solutions, and that takes too long. It's no good
> containing FindInstance, because my equations contain unknowns.
>
> To illustrate this last point, consider the input
>     FindInstance[a==b,a]
> I want Mathematica to return to me the solution
>     {{a->b}}
> but it doesn't -- it fails, because FindInstance can't cope with
> independent variables in the expression.
>
> So, I either need a watered-down Solve, that doesn't try to find every
> solution, or a beefed-up FindInstance, that doesn't mind about the
> independent variables.
>
> Thanks!
> Jamie.
>

There is a trick in [1] (by Peter Valko).
Replace b by a constant not related to your problem, apply FindInstance 
and substitute the chosen constant with b:

In[1]:= FindInstance[{a == b} /. b -> Catalan, a] /. Catalan -> b
Out[1]= {{a->b}}

Peter


[1] http://forums.wolfram.com/mathgroup/archive/2006/Sep/msg00207.html



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