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Re: Solve : missing elims in the Mathematica 8 version of the Mathematica 7 Solve[eqns,vars,elims]

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  • Subject: [mg115040] Re: Solve : missing elims in the Mathematica 8 version of the Mathematica 7 Solve[eqns,vars,elims]
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Wed, 29 Dec 2010 05:57:23 -0500 (EST)

On 28 Dec 2010, at 12:49, W. Deinhard wrote:

> ?Hi,
> in Mathematica 7 Solve allowed to specify the variables I wanted to eliminate.
> How can I do that in Mathtematica 8 ?
>
> The syntax is no longer
>
> Solve[eqns,vars,elims]
>
> but
>
> Solve[expr,vars,dom]
>
> Thanks , bye Walter.
>

First, the old syntax still works but now it is undocumented (?):

In[33]:== Solve[{1 ==== x^5 + y^5, a - b ==== x + y, b + a ==== x*y}, {x,
  y}, {a, b}]

Solve::svars:Equations may not give solutions for all "solve" variables. >>

{{y -> (1 - x^5)^(1/
      5)}, {y -> (-(-1)^(1/5))*(1 - x^5)^(1/5)},
   {y -> (-1)^(2/5)*(1 - x^5)^(1/5)},
   {y -> (-(-1)^(3/5))*(1 - x^5)^(1/5)},
   {y -> (-1)^(4/5)*(1 - x^5)^(1/5)}}

This, in fact, is the same answer as the one you get if you explicitly use Eliminate:

Solve[
 Eliminate[{1 ==== x^5 + y^5, a - b ==== x + y, b + a ==== x*y}, {a,
   b}], {x, y}]

Solve::svars:Equations may not give solutions for all "solve" variables. >>

 {{y -> (1 - x^5)^(1/
      5)}, {y -> (-(-1)^(1/5))*(1 - x^5)^(1/5)},
   {y -> (-1)^(2/5)*(1 - x^5)^(1/5)},
   {y -> (-(-1)^(3/5))*(1 - x^5)^(1/5)},
   {y -> (-1)^(4/5)*(1 - x^5)^(1/5)}}

I am not sure if the lack of documentation for the former usage is an oversight or it is now deprecated.

Andrzej Kozlowski


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