Update fit parameter limits


I would have a general question about setting parameter limits when using the Fitter class.
Let’s say I want to fit two parameters A and B. I also want to set limits to B in such a way that the lower limit for B is the value of A at the i-th step of the fit, while the upper limit is a fixed constant value.

Up to now I could not find any hint how to implement this iteration…any hint would be welcome!

Thanks in advance

maybe you can implement it by yourself in your function. For example, you add a line in your function with something like

So, if B takes a value that you do not want, your function returns a huge diverging value. The fit will test other values of B until the function returns a “correct” value.


thanks for the suggestion. Still the problem is that I don’t find the way to get the value of A along the fit steps…I can only get it in the end by calling the FitResult class, but it doesn’t help anymore!

In the end the question is: is there any way to get access to the fitted parameters DURING the fit, being then able to use them in order to set limits?

Is there a way to introduce a transformation on the parameters A and B in order to overcome this problem?
I mean if You have the lower limit on B being A, the new variable C=B-A will have the lower limit zero, right? The upper limit will then be const+A but You can just set it to the value You know it will never get, i.e. conts + maximum possible value of A.

I do understand that this is solution for the easiest example You provided but maybe it can help You in Your more complicated case :wink: