Re: symbolic derivatives
- To: mathgroup at christensen.cybernetics.net
- Subject: [mg333] Re: [mg320] symbolic derivatives
- From: Jerry Keiper <keiper>
- Date: Thu, 15 Dec 1994 14:43:20 -0600
> Although these functions are continuous, FindRoot gives an error
> message to the effect that the Jacobian matrix (needed for
> Newton's method), cannot be symbollically determined; it also
> suggests trying with 2 initial guesses insteadof one (so the
> secant method can be utilized). I conclude that Mathematica
> cannot differentiate continuously differentiable functions which
> are subject to conditions.
> I prefer to use Newton's method if possible. Does anyone know
> of a package thatwill solve nonlinear algebraic equations?
> Ideally such a package should allow one to provide the Jacobian
> matrix oneself.
You don't need a package. FindRoot already has an option to specify
the Jacobian. The default is Automatic, but you can specify it yourself
if it won't do it automatically.
In[1]:= FindRoot[Sin[Abs[x]] == 3/4, {x, 1},
Jacobian -> {{Sign[x] Cos[Abs[x]]}}]
Out[1]= {x -> 0.848062}
Jerry B. Keiper
keiper at wri.com
Wolfram Research, Inc.