symbolic derivatives
- To: mathgroup at christensen.cybernetics.net (mathgroup mathgroup)
- Subject: [mg320] symbolic derivatives
- From: Edward Birchfield <edward at atlantic.earth.nwu.edu>
- Date: Mon, 12 Dec 1994 13:47:19 CST
Dear Mathgroup members,
I am trying to utilize FindRoot to solve a system of nonlinear algebraic
equations. Involved in these equations are some very simple conditional
functions. For example:
mi1[ts1_,vice_] := 0. /; ts1 < tscrit || vice <= 0.
mi1[ts1_,vice_] := gammats1 (ts1-tscrit)(1 - Exp[mlam (ts1-tscrit)] /;
ts1 >= tscrit && vice > 0.
where gammts1, mlam and tscrit are constants.
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 instead
of 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 that
will solve nonlinear algebraic equations? Ideally such a package should allow
one to provide the Jacobian matrix oneself.
Edward Birchfield