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?
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