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.
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Robert K. Schaefer Email: bob@milkyway.gsfc.nasa.gov
NASA/GSFC Code 664 Phone: 301-286-0878
Greenbelt, MD 20771 FAX: 301-286-1629
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