ROOT   Reference Guide
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multifit.py
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1## \file
2## \ingroup tutorial_pyroot
3## \notebook
4## Example showing how to fit in a sub-range of an histogram
5## An histogram is created and filled with the bin contents and errors
6## defined in the table below.
7## 3 gaussians are fitted in sub-ranges of this histogram.
8## A new function (a sum of 3 gaussians) is fitted on another subrange
9## Note that when fitting simple functions, such as gaussians, the initial
10## values of parameters are automatically computed by ROOT.
11## In the more complicated case of the sum of 3 gaussians, the initial values
12## of parameters must be given. In this particular case, the initial values
13## are taken from the result of the individual fits.
14##
15## \macro_output
16## \macro_code
17##
18## \author Wim Lavrijsen
19
20from ROOT import TH1F, TF1
21from ROOT import gROOT
22from array import array
23
24x = ( 1.913521, 1.953769, 2.347435, 2.883654, 3.493567,
25 4.047560, 4.337210, 4.364347, 4.563004, 5.054247,
26 5.194183, 5.380521, 5.303213, 5.384578, 5.563983,
27 5.728500, 5.685752, 5.080029, 4.251809, 3.372246,
28 2.207432, 1.227541, 0.8597788,0.8220503,0.8046592,
29 0.7684097,0.7469761,0.8019787,0.8362375,0.8744895,
30 0.9143721,0.9462768,0.9285364,0.8954604,0.8410891,
31 0.7853871,0.7100883,0.6938808,0.7363682,0.7032954,
32 0.6029015,0.5600163,0.7477068,1.188785, 1.938228,
33 2.602717, 3.472962, 4.465014, 5.177035 )
34
35np = len(x)
36h = TH1F( 'h', 'Example of several fits in subranges', np, 85, 134 )
37h.SetMaximum( 7 )
38
39for i in range(np):
40 h.SetBinContent( i+1, x[i] )
41
42par = array( 'd', 9*[0.] )
43g1 = TF1( 'g1', 'gaus', 85, 95 )
44g2 = TF1( 'g2', 'gaus', 98, 108 )
45g3 = TF1( 'g3', 'gaus', 110, 121 )
46
47total = TF1( 'total', 'gaus(0)+gaus(3)+gaus(6)', 85, 125 )
48total.SetLineColor( 2 )
49h.Fit( g1, 'R' )
50h.Fit( g2, 'R+' )
51h.Fit( g3, 'R+' )
52
53par1 = g1.GetParameters()
54par2 = g2.GetParameters()
55par3 = g3.GetParameters()
56
57par[0], par[1], par[2] = par1[0], par1[1], par1[2]
58par[3], par[4], par[5] = par2[0], par2[1], par2[2]
59par[6], par[7], par[8] = par3[0], par3[1], par3[2]
60
61total.SetParameters( par )
62h.Fit( total, 'R+' )
1-Dim function class
Definition TF1.h:213
1-D histogram with a float per channel (see TH1 documentation)}
Definition TH1.h:575