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Local minima possible. lsqnonlin stopped because the size of the current step is less than the selected value of the step size tolerance.

Asked by Prakash Packirisamy on 9 Feb 2019
Latest activity Answered by Alan Weiss
on 12 Feb 2019
I am using lsqnonlin solver for a non-linear data fitting problem.
I get a result which says "Local minima possible. lsqnonlin stopped because the size of the current step is less than the selected value of the step size tolerance".
I have a couple of questions on this regard.
  1. After displaying the above warning, lsqnonlin gives a solution which is very close to my initial conditions to the parameter values. Why does this happen ?
  2. What is the difference between local minima possible and local minima found while using these solvers ?
  3. What should i change in optimoptions to find the local minima using lsqnonlin ?
  4. How to calculate the standard error of parameter estimates using lsqnonlin ?
I have tried decreasing the function tolerance to 1E-10.
I have also tried decreasing the stepsize tolerance to 1E-10.
Neither of them worked.
What am i missing here ?
I kindly request you to help me in this regard.
Thanks and with best regards,
Prakash

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2 Answers

Answer by Alan Weiss
on 11 Feb 2019
 Accepted Answer

Take a look at some suggestions in When the Solver Might Have Succeeded and When the Solver Succeeds.
Alan Weiss
MATLAB mathematical toolbox documentation

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Thanks a lot Alan Weiss for your recommendations.
I found it helpful.
I have one more follow up question along the same line.
  1. How to determine the standard error of the parameter estimates using lsqnonlin
Thanks once again.
With regards,
Prakash

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Answer by Alan Weiss
on 12 Feb 2019

Perhaps this old example will be helpful. But maybe it is better to use nlparci from Statistics and Machine Learning Toolbox™.
Alan Weiss
MATLAB mathematical toolbox documentation

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