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MathGroup Archive 2005

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Re: Solve yields unreal solutions, NSolve yields real solutions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg58287] Re: Solve yields unreal solutions, NSolve yields real solutions
  • From: Peter Pein <petsie at dordos.net>
  • Date: Sun, 26 Jun 2005 01:33:49 -0400 (EDT)
  • References: <d9issf$cps$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Mukhtar Bekkali schrieb:
> I thought NSolve is the same as Solve just numeric. The below code
> gives real answers, replacing NSolve with Solve in the last line
> generates Unreal results.  I do not understand why.
> 
> \!\(\*
>   RowBox[{\(Clear["\<Global`*\>"]\), "\n", \(Remove["\<Global`*\>"]\),
...

>     "\[IndentingNewLine]", \(NSolve[FOCB \[Equal] 0, T\_b]\)}]\)
> 

I do not use RealOnly, so I can not tell you exactly what's going on,
but I *guess* the intermediate complex numbers vanish due to RealOnly.

 Solve gives me only Reals in this case:

sol = RootReduce[Solve[FOCB == 0, Subscript[T, b]]]];
N[sol]

{{Subscript[b, 1] -> 1.8560333600623977,
  Subscript[b, 2] ->  9.206972531099007},
{Subscript[b, 1] ->  0.3071686114422483,
 Subscript[b, 2] ->  0.9103220918432908},
{Subscript[b, 1] ->  -8.463201971504645,
 Subscript[b, 2] ->  -0.8172946229422982}}

I *guess* the intermediate complex numbers vanish due to RealOnly.
-- 
Peter Pein
Berlin


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