Hi eddy, you are right, I've tested it first with 3 parameters and then omitted one and forgot to include it again in the example. After trying somewhat more I think I've found the problem : when I do a lego plot of my fit, and afterwards a lego plot of my histogram, the histogram is rescaled to the axes of the fit plot.....therefore I misinterpreted the result. For now I think the fit is probably OK but I want to get rid of the rescaling to make sure. Do you know a solution for that? many thanks in advance, S. Eddy Offermann wrote: > 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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