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MathGroup Archive 2007

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Re: How to choose real positive solutions?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg74309] Re: How to choose real positive solutions?
  • From: "dimitris" <dimmechan at yahoo.com>
  • Date: Sun, 18 Mar 2007 00:45:49 -0500 (EST)
  • References: <etg46h$ijg$1@smc.vnet.net>

Hi Manfred.
You should have posted also your system of equations.
In this way we would have helped us very much!

Ayway...

Copy/Paste the following in a notebook, select the cell and press Shift
+Enter

Print[StyleForm["a system of three equations in three unknowns",
FontColor -> Blue]]
eq1 = x + y + 10*z^7 == 5
eq2 = -4*x^2 - y + 2*z^3 == 0
eq3 = 6*x^2 + 5*y^7 + 4*z == 11
roots = NSolve[{eq1, eq2, eq3}, {x, y, z}];
Print[StyleForm["the number of solutions", FontColor -> Blue]]
Length[roots]
Print[StyleForm["a shorted form of", FontColor -> Blue, FontSlant ->
Italic], StyleForm[" solutions", FontColor -> Blue]]
Short[roots, 10]
Print[StyleForm["only positive solutions", FontColor -> Blue]]
Cases[{x, y, z} /. roots, {(a_Real)?Positive, (b_Real)?Positive,
(c_Real)?Positive} :> {x -> a, y -> b, z -> c}]


Regards
Dimitris


mandix wrote:
> Hi,
> suppose I want to solve a system of 3 equations and 3 unknowns
> (polynomial of degree whatever, say n). Is there a way to tell NSolve
> to return only real and positive solutions (and ignore the rest)?
>
> thanks you so much,
>
> Manfred



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