MathGroup Archive 2005

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

Search the Archive

Re: solve output "problem"

  • To: mathgroup at smc.vnet.net
  • Subject: [mg59659] Re: solve output "problem"
  • From: Paul Abbott <paul at physics.uwa.edu.au>
  • Date: Tue, 16 Aug 2005 04:56:58 -0400 (EDT)
  • Organization: The University of Western Australia
  • References: <dc76fj$jrc$1@smc.vnet.net> <dchnth$7vb$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

In article <dchnth$7vb$1 at smc.vnet.net>,
 Selina <yedekaccount at hotmail.com> wrote:

> Actually, I was looking for a way to get a symbolic representation of the 
> roots which I could then see how they change with respect to some parameters, 
> so NSolve wasn't my first choice. But I guess I'll have to resort to that.

I don't understand your conclusion. Root _is_ a symbolic representation 
of the root and it does allow you to see how they change with respect to 
some parameters. For example, here is a simple polynomial involving one 
parameter, a.

  sol = Solve[x^5 + a x + 1 == 0, x]

For the first root,

  r[1][a_] = x /. sol[[1]]

Here we plot r[1][a] for -5 < a < 4.

  Plot[r[1][a], {a, -5, 4}]

Also, let's compute the derivative of this root with respect to a.

  dr[1][a_] = D[r[1][a], a]

Note that this is an exact symbolic representation of the derivative. 
(It can be reduced to a root of a 5th order polynomial, but RootReduce 
or FullSimplify cannot do this simplification).
 
Here we plot dr[1][a] for -5 < a < 4.

  Plot[dr[1][a], {a, -5, 4}]

Cheers,
Paul

-- 
Paul Abbott                                      Phone: +61 8 6488 2734
School of Physics, M013                            Fax: +61 8 6488 1014
The University of Western Australia         (CRICOS Provider No 00126G)    
AUSTRALIA                               http://physics.uwa.edu.au/~paul
        http://InternationalMathematicaSymposium.org/IMS2005/


  • Prev by Date: Re: NSolve problem
  • Next by Date: Re: Advanced symbolic Integration using Mathematica
  • Previous by thread: Re: Re: solve output "problem"
  • Next by thread: Re: Mathematica's CPU utilization