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RE: positive root only using Solve[]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg41821] RE: [mg41791] positive root only using Solve[]
  • From: "John C. Erb, Ph.D." <John_C_Erb at prodigy.net>
  • Date: Fri, 6 Jun 2003 09:50:52 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Hello,

Will
		Select[x /. Solve[x^2 - 1 == 0, x], # > 0&]

do what you want?

For more general equations you might need to specify
that x is to be Real as well as positive.

 Select[x/.Solve[x^2-1\[Equal]0,x],(#\[Element]Reals&&#>0)&]

John C. Erb
email: John_C_Erb at prodigy.net




-----Original Message-----
From: seferiad [mailto:seferiad at pacbell.net]
To: mathgroup at smc.vnet.net
Subject: [mg41821] [mg41791] positive root only using Solve[]


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


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