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Re: positive root only using Solve[]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg41841] Re: positive root only using Solve[]
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Fri, 6 Jun 2003 09:51:23 -0400 (EDT)
  • References: <bbnaqt$2e2$1@smc.vnet.net>
  • Reply-to: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Sender: owner-wri-mathgroup at wolfram.com

"seferiad" <seferiad at pacbell.net> wrote in message
news:bbnaqt$2e2$1 at smc.vnet.net...
> Hello,
> Consider the following equation.
>
> Solve[x^2 ==1, x]
>
> Mathematica will output 1 and -1 for x.  However, I only want Mathematica
to
> output the positive solution (i.e., x -> 1), so I can use this
conveniently
> in a subsequent equation. Is there a way to force the output to produce
only
> the positive solution?  Thanks, Jay
>


seferiad,
Three observations:

    Simplify[x^2 == 1 && x >= 0]

        x == 1


    Select[Solve[x^2 == 1, x], #1[[1,2]] > 0 & ]

        {{x -> 1}}


    << "Algebra`InequalitySolve`"

    InequalitySolve[x^2 == 1 && x >= 0, x]

        x == 1

--
Allan
---------------
Allan Hayes
hay at haystack.demon.co.uk
Voice: +44 (0)116 241 8747
Fax: +44 (0)870 164 0565


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