Dear all,

I have the following problem:

In some fits using Artemis (Demeter 0.9.25) I will get negative values for parameters where it makes no sense at all. For example, when trying to fit two first shell paths, Pt-Pt and Pt-O, for a Pt nanoparticle,
sigma^2 for the Pt-O path becomes negative.

Obviously, sigma^2 has to be a positive number.

My questions:

1. Why does the fit algorithm do this?

2. What can I do to avoid this?

I know that there are most likely significant problems with my fit if this behaviour occurs. As far as I know it's possible to impose restrictions in Artemis and if anyone could point me towards a tutorial explaining how to implement restrictions that might be a first step in the right direction. Currently, the chapter "Constraints and restraints" in the Artemis documentation is "Coming soon......".

With kind regards,


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