Fitting

HOME > RUNNING GRSISORT > ANALYSIS > FITTING

As part of the GRSISort analysis package, there are a number of classes and methods available for fitting:

For gamma-ray peaks

• GGaus Used to fit peaks with a gaussian and a linear background. This class is used when the 'g' key is used on a GCanvas (see Canvas Hotkeys).
• GPeak Used to fit peaks with a gaussian + skewed gaussian and a background of a step function + constant. This class is used when the 'f' key is used on a GCanvas (see Canvas Hotkeys).
• TPeak Used to fit peaks with a gaussian + skewed gaussian. This class is used when the 'F' key is used on a GCanvas (see Canvas Hotkeys).
• TPeakFitter This is a versatile class than can fit any number of peaks of different shapes plus a global background (by default a quadratic polynomial). Each peak has to be added individually and can be one of the classes derived from TSinglePeak:
  • TGauss - a simple gaussian.
  • TRWPeak - a radware like peak.
  • TABPeak - an addback peak with two different gaussians for single hits and double hits.
  • TAB3Peak - an addback peak with three different gaussians for up to three hits.

Below is a comparions of different fits of a standard photopeak with or without including a skewed gaussian:

In order to fix parameters of specific peaks, use the fit function of the peak:

TPeakFitter pf(<low range>,<high range>);
TRWPeak peak(<centroid>);
pf.AddPeak(&peak);
TF1* peakFunc = peak.GetFitFunction();
peakFunc->FixParameter(<index>, <value>);
pf.Fit(<histogram>);

To get a list of the parameters use the TF1::Print("v") function (peakFunc->Print("v") in the example above). To access parameters of the global background function use TPeakFitter::GetBackground() (pf.GetBackground()->FixParameter(<index>, <value>) in the example above). See also #1262.

For decay curves

• TDecay Used to fit nuclear decay curves.