Re: [ROOT] multidimensional/multicorrolated/multiconstrained fit

From: Rene Brun (brun@pcbrun.cern.ch)
Date: Sat Nov 06 2004 - 23:01:12 MET


Hi Martin,

A possible solution could be via THStack and implement THStack::Fit.
A THStack is a list of histograms. 
The existing fitting algorithms (H1FitChisquare and H1FitLikelihood)
could be extended to support a THStack.

If somebody has a better idea, let me know.

Rene Brun

On 
Sat, 6 Nov 2004, schulte-wissermann wrote:

> hi all ROOTers,
>  consider the following problem:
>   - you have a signal (e.g. missing-mass-spektrum) which is 
>     parameterized by a Lorentz convoluted with a Gaus. 
>     the signal is on some kind of background wich you emulate by a 
>     cubic function. after the fit i get as a result (let's say) seven 
>     parameters.
> 
>     NO PROBLEM SOFAR: see the famous FittingDemo and langaus tutorials.
> 
>     now the problem:
>      i now split my data considering another observable (let's say ten 
>      missing-mass distributions as a function of an angle of an ejectile).
>      i now have to fit ten INDIVIDUAL histos, however physics tells me 
>      that the fits are correlated:
>       - the parameters should be 'some' smooth function of the additional observable.
>       - the probability of the fits should be 'some' smooth function of the additional observable.
>       - the sum of all signals should match the integral of the total signal. 
>      
>   now the question:
>      how can i simultaniously fit the ten histos? is there a ROOT-class?
>      are there some examples? one could think of some 
>      multi-constraint, iterative fitting method; or one could try to
>      fit the surface of a TH2F filled with 
>         h->Fill(missingmass, angle, totalcountsofthisbin).   
>      i'm currently working on this problem, but the output is not yet what i'm aiming for. 
>  
> thanx in advance,
>   martin
> 



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