Hi Steven, It seems that for your fitting function only the ratio (!) [0]/[1] is relevant. So now you are trying to fit two 100% correlated variables. What aws the "convergence" state of the fit ? Eddy > > > > I'm using ROOT for the analysis of my nuclear medicine Monte Carlo > > simulations results. Therefore I want to fit a twodimensional function > > to a 2D histogram. I therefore use the following code: > > > > #include "TF2.h" > > #include "TH2.h" > > > > void fit2d(){ > > TFile b("t4.root"); > > > > Singles->Draw("PosZ:PosX>>hnew(18,0,180,20,-200,200)"); > > > > TF2 *f2e = new TF2("f2e", > > "([0]*(y+201))/([1]*(x^2+(y+201)^2))",-0.5,180.5,-201,201) ; > > > > f2e->SetParameters(1,1) ; > > > > hnew->Fit("f2e") ; > > > > hnew->Draw("LEGO") ; > > > > f2e->Draw("LEGO same"); > > } > > > > The result I get is not satisfactory however as I see that the maxima of > > the histogram and the fit are put equal. This is of course not the most > > appropriate fit as can be seen from the attached gif. The wireframe > > plot is the data while the filled lego plot is the fit. > > > > In fact I was wondering how I could change the criteria in TH2F::Fit to > > optimalize my 2D fit, as I have the impression now that it is mainly > > penalizing the maximum deviation. > > > > Thanks in advance, > > > > best regards, > > > > Steven > > > > S. Staelens > > Ghent University > > ELIS / Medisip > > Proeftuinstraat 86 > > B-9000 Gent > > tel. 0032 9 264 66 28 > > fax. 0032 9 264 66 18 > > email: Steven.Staelens@rug.ac.be
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