TGraphFit.py

#
# Draw a graph with error bars and fit a function to it
#
from ROOT import gStyle, TCanvas, TGraphErrors
from array import array
gStyle.SetOptFit (111) # superimpose fit results
c1=TCanvas("c1" ,"Data" ,200 ,10 ,700 ,500) #make nice
c1.SetGrid ()
#define some data points . . .
x = array('f', (-0.22, 0.1, 0.25, 0.35, 0.5, 0.61, 0.7, 0.85, 0.89, 1.1) )
y = array('f', (0.7, 2.9, 5.6, 7.4, 9., 9.6, 8.7, 6.3, 4.5, 1.1) )
ey = array('f', (.8 ,.7 ,.6 ,.5 ,.4 ,.4 ,.5 ,.6 ,.7 ,.8) )
ex = array('f', (.05 ,.1 ,.07 ,.07 ,.04 ,.05 ,.06 ,.07 ,.08 ,.05) )
nPoints=len ( x )
# . . . and hand over to TGraphErros object
gr=TGraphErrors ( nPoints , x , y , ex , ey )
gr.SetTitle("TGraphErrors with Fit")
gr.Draw ( "AP" ) ;
gr.Fit("gaus")
c1.Update ()
# request user action before ending (and deleting graphics window)
raw_input('Press <ret> to end -> ')