Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2006
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2006

[Date Index] [Thread Index] [Author Index]

Search the Archive

Selecting Real Roots, Again

  • To: mathgroup at smc.vnet.net
  • Subject: [mg67104] Selecting Real Roots, Again
  • From: "DOD" <dcodea at gmail.com>
  • Date: Fri, 9 Jun 2006 01:08:55 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

I've read the many posts already here about how to get mathematica to
select real roots for you, but I have a slightly(very slighty, I
thought) different problem ,and I don't know how to get mathematica to
do what I want.

I want to get the solution for a polynomial of the following form:
d x^n + (1-d) x^2 =y

so for example, I do
Solve[.9 x^10 + .1 x^2 ==y,x]
and I get a whole bunch of solution,  very good.  For my purposes, y
lives in the [0,1], as must the solution.  So I can see, by hand, which
root I want; exactly one root is both real, and has solutions in my
inverval.  So I want to tell mathematica to:

A: look at only solutions x* that are real over y in [0,1]

and

B: of those solutions, give the one x* that itself lies is [0,1].

So, when I try to do something from reading previous posts, I cannot
get it to work:
In[24]:=
Select[Solve[.9 x^10 + .1 x^2 ==y,x],Element[x/.#,Reals]&]

Out[24]=
{}
or perhaps
In[41]:=
Select[Solve[.9 x^10 + .1 x^2
==y,x],Assuming[Element[y,Reals],Eement[x/.#,Reals]]&]
Out[41]=
{}


 So How to I tell mathematica to do this?


  • Prev by Date: Formatted Date String
  • Next by Date: RE: Plotting Cosh(x)?
  • Previous by thread: Re: Formatted Date String
  • Next by thread: Re: Selecting Real Roots, Again