Solving a nonlinear algebraic equations using fsolve or a defined function

Hi,

I use fsolve to solve a system of nonlinear algebraic equations. My general question is that Is fsolve strong enough to find a solution for such a system? If I cannot find the solution using fsolve, Does it mean no other methods are able to solve it?!

Which method can I use instead of fsolve?

Thank you, Regards

Answer 1

[Walter Roberson]

fsolve() relies upon the initial point you give it. It offers three different algorithms with different good points and bad points.

For example Levenberg-Marquardt can be good dealing in changes of direction and for getting around minor "hills", but it can still get caught in steep enough valleys (every direction looks very bad) or even in broad enough valleys (climbing out would require exceeding the stepsize maximum).

Sometimes vpasolve() from the symbolic toolbox can reason better, but certainly not always.

In some cases a useful approach can be using solve() to get a solution in terms of rootof() operators, and then to chase solutions to the rootof() such as with vpasolve() or fsolve() .

Generally speaking, finding the roots of nonlinear equations involving trig functions can be difficult.

[sina]

Walter, Thank you for your comprehensive answer.