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MathGroup Archive 2005

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Re: How to use "Solve" to get only real number solutions?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55140] Re: [mg55132] How to use "Solve" to get only real number solutions?
  • From: "Christoph Lhotka" <lhotka at astro.univie.ac.at>
  • Date: Mon, 14 Mar 2005 03:43:39 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Hi there is a package, which redefines all functions, so that you only get
real valued solutions called RealOnly

You load it into your Mathematica Session with

In[..]:=Needs["Miscellaneous`RealOnly`"]

Now you will get only real answers...

Another option is to use the function Select...

In[..]:=Solve[...]
Out[...]:={x->,x->,...}

In[..]:=Select[%,FreeQ[#[[2]], I * _]&]
Out[..]:=...

Or use DeleteCases to delete all expression holding imaginary parts.

best wishes...

On Sun, 13 Mar 2005 04:57:54 -0500 (EST)
 "PengYu.UT at gmail.com" <PengYu.UT at gmail.com> wrote:
> Hi All
> 
> For example I have the following function and I want to find the
> solution of the quation shown below. But Mathematica showns not only
> real number solutions. Do you know how to restrict the solutions to
> only real numbers. Thanks!
> 
> Best wishes,
> Peng
> 
> intensity[x_, δ_, p_, λ_] := 1/4 + (2*Cos[(Pi*x)/100])/Pi +
> (4*Cos[(Pi*x)/100]^2)/Pi^2 - (2*Cos[(3*Pi*x)/100])/(3*Pi) -
>  (8*Cos[(Pi*x)/100]*Cos[(3*Pi*x)/100])/(3*Pi^2) +
> (4*Cos[(3*Pi*x)/100]^2)/(9*Pi^2)
> 
> Solve[intensity[x, 0, 200, 50] == 0.3*(1/4 + 32/(9*Pi^2) +
> (4*Sqrt[2])/(3*Pi)), x]
> 


-- Christoph Lhotka --
University of Vienna
Institute for Astronomy
Tuerkenschanzstr. 17 
1180 Vienna, Austria
fon. +43.1.4277.518.41
mail. lhotka at astro.univie.ac.at


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