I am deliberately not including data or a model for this question, as I want a more general answer so that I may be able to trouble shoot this myself in the future.
When performing a fit, usually a fit with more than two parameters, I occasionally see the error message:
The step size in the search has become less than the tolerance prescribed by the PrecisionGoal option, but the gradient is larger than the tolerance specified by the AccuracyGoal option. There is a possibility that the method has stalled at a point that is not a local minimum.
More often than not, the fit looks good by eye, and the fitted parameter values are reasonable.
So the questions are:
- What does this error really mean?
- Does it matter, especially if the fit looks good and the fit parameters are reasonable? That is, how trust worthy are the results?
- How can one prevent this error? I have often played with
AccuracyGoalbut it doesn't seem to have much of an effect.
I appreciate this problem will have solutions that vary depending on the individual case, but I often fit with very different models and would like some advice on how to avoid such errors, and trouble shoot them myself -- rather than just post the problem here.