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MathGroup Archive 1999

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Re: Real roots and other assumptions...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19917] Re: [mg19883] Real roots and other assumptions...
  • From: "David Park" <djmp at earthlink.net>
  • Date: Tue, 21 Sep 1999 02:22:50 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Janus,

This works for low order polynomials:

In[10]:=
Select[Solve[-24 + 4*x - 2*x^2 + x^3 + x^4 == 0], 
  FreeQ[#1, Complex] & ]
{{x -> -3}, {x -> 2}}

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/

>Hi,
>I keep encountering problems of the following type when using mathematica:
>I want to solve some equation(s) under some assumptions about the unknown(s),
>e.g. find the real roots of (x-1)(x^2+1).
>I've tried Solve[{Im[x]==0,(x-1)(x^2+1)==0},x]] for the above problem, but that
>doesn't get me anywhere.
>
>Is there a general way to let Mathematica know about such additional bounds as
>non-complexness etc? -- if so I would be happy to know it!
>
>Janus Wesenberg
>Student of Physics.
>
>PS. I'm using Mathematica from a HP-UX 10 system, and the notebook interface
>have grave difficulties handling large expressions (they scrambled to complete
>nonsense). The local system administrator just says "Use the text access", but
>does anyone know how to make the notebook interface work?
>
>



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