Re: FindRoot Related Question
- To: mathgroup at smc.vnet.net
- Subject: [mg28502] Re: FindRoot Related Question
- From: Daniel Lichtblau <danl at wolfram.com>
- Date: Sun, 22 Apr 2001 21:03:18 -0400 (EDT)
- Organization: Wolfram Research, Inc.
- References: <email@example.com>
- Sender: owner-wri-mathgroup at wolfram.com
Don Paddleford wrote:
> I have been unable to get FindRoot to run on simultaneous equations which
> include terms such as Sign[x-x] or UnitStep[x-x]. When I
> checked to see if the equations accidently contained some undefined variable
> (using Variables[on equation terms] I was surprised the list of variables
> included Sign or UnitStep of [x-x] as well as the true variables like
> x and x. How get around this?
> Don Paddleford
Variables will not tell you how FindRoot regards your expression.
My guess is that FindRoot will prefer real-analytic functions. At the
very least, don't try this with just one starting value; you'll want to
use a secant method, so specify two values.
To get real-analytic functions, you might use
which are correct almost everywhere for real-valued f.
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