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Re: Solve problem

  • To: mathgroup at smc.vnet.net
  • Subject: [mg98041] Re: [mg97988] Solve problem
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Sat, 28 Mar 2009 05:45:43 -0500 (EST)
  • Reply-to: hanlonr at cox.net

a1 /. Select[{{b1 -> -2, a1 -> -1}, {b1 -> 0.5, a1 -> 3}}, 
  (a1 /. #) > 0 &]

{3}

Cases[{{b1 -> -2, a1 -> -1}, {b1 -> 0.5, a1 -> 3}},
 (a1 -> x_ /; x > 0) :> x, Infinity]

{3}

Or instead of using Solve use Reduce and include constraint on a1


Bob Hanlon

---- Bruno Campanini <BC at gmail.com> wrote: 

=============
I have a Solve[...] which gives me solutions like
{{b1 -> -2, a1 -> -1 }, {b1 -> 0.5, a1 -> 3}}
or like
{{a1 -> 1, b1 -> 3}}

How can I get the positive value for a1, which is  3
in the first case and  1  in the second one?

Bruno




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