Re: FindRoot with algebraic expressions
- To: mathgroup at smc.vnet.net
- Subject: [mg122847] Re: FindRoot with algebraic expressions
- From: Bill Rowe <readnews at sbcglobal.net>
- Date: Sat, 12 Nov 2011 07:34:34 -0500 (EST)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
On 11/11/11 at 4:54 AM, dashiell at web.de (Mirko) wrote:
>I was wondering how FindRoot works when trying to use a algebraic
>initial point. I.e.:
>FindRoot[h[theta]==0,{theta[m], ???}] where h is function of theta,
Are you aware FindRoot is designed to return numeric answers not
algebraic answers? Also, in Mathematica, theta[m] is interpreted
as the *function* theta evaluated at m, i.e., not a variable.
That is
FindRoot[h[theta]==0 {theta[m]
is asking Mathematica to find the root of the function h with
respect to the function theta, probably not what you mean.
If theta were defined, then it should be possible to do
FindRoot[h[theta] == 0, {m, m0}]
assuming theta was defined using Set (not SetDelayed) and m0 is
given a numeric value. The above would return a value for m that
makes h[theta] 0.
>for example:
>h[theta_]=1/(1-m)*theta[m] (notice that this is for a given m).
What are you expecting here? Until theta is defined, the only
possible solution is the trivial solution, i.e., theta[m] is 0
>What should I use as a starting point?
Someone here likely can help you if you post details of the
problem you are actually trying to solve. If you are trying to
find a symbolic root to an expression, you need something other
than FindRoot which is a numeric function.