Piecewise fits

[mwilkins]

I would like to do a fit (preferably in RooFit) using a smooth piecewise function. I’m having trouble finding documentation on this. Sorry for the broadness of the question, but is there any built-in way to do this?

[Wile_E_Coyote]

Numerical Minimization

[mwilkins]

Sorry, but I’m not entirely clear on the relevance of that page. Were you pointing out the “RosenBrock” function they build in the examples?

[moneta]

Sorry, you should be more precise on what you would like to do :

• minimising a function ? (in this case the Rosenbrock example can be instructive)
• fitting a data points with a function and use RooFit ?

You can look also at the ROOT primer and at the various course material which is linked from the ROOT Web page for this general questions

Lorenzo

[mwilkins]

I’m trying to fit to an awkwardly shaped histogram. I would like to specify a few different shapes to be fit to different parts of the histogram and constrain these shapes to be smooth numerically at the boundaries between them.

I have not found any documentation that seems particularly relevant to this.

[moneta]

Hi,

In this case the best is you create your own global function, that evaluates differently depending on the range and you put the smooth constraint in defining this function.
It is a problem a user needs to solve

Lorenzo

[YanXL]

Try this:

Piecewise function fits of TH1F

Hi all, I am trying to fit a combination of TF1’s to a ratio represented by a TH1F to make a piecewise fit parameterising this ratio for later use (an example of the ratio and fits in attachment). fit.pdf (29.6 KB) I tried using three separate TF1’s defined over three separate intervals to piece-wise define the various parts of the TH1F, but this naturally has discontinuities at the boundaries. I thought the way around this would be to define another function which was the combination of all…