MATLAB Curve Fitting - Output Results

Hello.

I am using MATLAB Curve Fitting toolbox to get an equation relating 2 variables, each one is an array of n elements.

Accidentally, I discovered that the Curve Fitting Tool window does not give the same outputs when I repeat the fitting procedure.

Both variables do not change their values and the only thing I do is to refresh one of the variables at the Curve Fitting Tool ( using the dropbox available ).

Is this normal?

If yes, Must I use the fitting outputs parameters of the first interaction?

If no, what can i doing wrong?

Thank you.

Best Regards,

Answer 1

[John D'Errico]

Is this normal to have happened, that the results can change when you redo the procedure? Yes.

Did you supply starting values for the parameters to be estimated? If not, then fit uses RANDOM starting values. They will not converge to exactly the same result. If you change the start point in an optimization, then the end point can vary. That is true for any numerical optimization tool. So, YES, it is normal.

[santos666]

Hello John.

I did not supply starting values.

Thank you.

Best Regards.

[John D'Errico]

Then it used a random start, so the result can vary, usually subtly, but still not exactly the same to full precision. In some cases, it will generate a completely different solution, if the problem has multiple local minimizers.