Hello, I seemed to find 2 problems while using root to fit histograms. 1) Funny behavior in fitting sums of functions when a landau function is involved, and 2) Getting the SetOptFit to display the parameters as described. 1) I tried fitting a sum ("total") of a landau function and an exponential TH1F *hist; // fitting functions TF1 *exp1, *land, *total; // fitting parameters Double_t par[5]; land = new TF1("land", "landau(0)",20,800); hist->Fit(land,"WQ0","",300,800); hist->Fit(exp1,"WQ0+","",20,200); exp1 = new TF1("exp1","expo(0)", 20, 800); land->GetParameters(&par[0]); exp1->GetParameters(&par[3]); total->SetParameters(&par[0]); total = new TF1("total","expo(3)+landau(0)", 20, 800); hist->Fit(total,"WR"); This works fine unless I try to do the fitting with the exponential parameters FIRST in the parameter list, i.e., land->GetParameters(&par[2]); exp1->GetParameters(&par[0]); total->SetParameters(&par[0]); total = new TF1("total","expo(0)+landau(2)", 20, 800); hist->Fit(total,"WR"); In which case the fit fails, complaining that the ERROR MATRIX IS NOT POSITIVE DEFINITE. 2) Fit parameters not being displayed According to the documentation: gStyle->SetOptFit(0101); should print the names/values of the parameters AND the Chi-squared. It does not print the chi-squared, although it does print the parameters. However, if I use gStyle->SetOptFit(10101); it prints both chi sq and the parameters?! Thanks, Bob Schaefer Root 3.1/02 on LinuxPPC2000 running on a Mac G4 dual processor. ---------------------------------------------------------- Robert K. Schaefer Email: bob@milkyway.gsfc.nasa.gov NASA/GSFC Code 664 Phone: 301-286-0878 Greenbelt, MD 20771 FAX: 301-286-1629 ----------------------------------------------------------
This archive was generated by hypermail 2b29 : Tue Jan 01 2002 - 17:51:00 MET