Fsolve and initial guesses

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Selim Elbadri
Selim Elbadri 2023-5-28
移动：Torsten 2023-5-28
Hi,
I have a system of nonlinear equations and corresponding variabls that I need to solve for. I use the 'fsolve' function and I get the following message from MATLAB:
Equation solved, inaccuracy possible.
The vector of function values is near zero, as measured by the value
of the function tolerance. However, the last step was ineffective.
<stopping criteria details>
I noticed that the solutions change a bit - at least some variables qualitatively - once I change initial guesses. I keep getting the same message as above but qualitatively different solutions when I increase all initial guesses by 10% and again when I decrease all guesses by 10%. How worried should I be?

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回答（1 个）

Torsten
Torsten 2023-5-28
移动：Torsten 2023-5-28
You already received several responses for this question here:
https://uk.mathworks.com/matlabcentral/answers/1973704-interpreting-the-results-of-fsolve?s_tid=prof_contriblnk
Iterative processes keep the risk of converging to no solution or to a wrong solution. So the only way to decide "how worried you should be" is to look at the solution, see whether it makes physical sense and compute whether it gives a residual near zero when inserted into your system of equations.

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