How to use pyROOT 応用編 その3

任意関数での ヒストグラムの fitting

#/bin/usr/env python

import sys, math
import ROOT


class Linear:
    def __call__(self, x, par):
        return par[0] + x[0] * par[1]

if __name__=='__main__':

    cv  = ROOT.TCanvas("cv", "Fitting Example", 200, 10, 700, 500)

    # create a linear function for fitting
    f = ROOT.TF1('f', Linear(), -1., 1., 2)

    # create histogram ( identify, Title, ?, xmin, xmax )
    h = ROOT.TH1F('h', 'px', 100, -1., 1.)
    f2= ROOT.TF1('f2', '6. + x * 4.5', -1, 1.)

    h.FillRandom('f2', 10000)
    

    # fits the hitstogram with the 'Linear' function
    h.Fit(f)

    # export
    cv.Print("graphtest4.png")

    # print results
    par = f.GetParameters()
    print 'fitting result: const = ', par[0], ', pitch = ', par[1]

実行結果

$ python graphtest4.py
 FCN=101.388 FROM MIGRAD    STATUS=CONVERGED      29 CALLS          30 TOTAL
 EDM=2.65063e-16    STRATEGY= 1      ERROR MATRIX ACCURATE
  EXT PARAMETER                                   STEP         FIRST
  NO.   NAME      VALUE            ERROR          SIZE      DERIVATIVE
   1  p0           9.89861e+01   9.94918e-01   4.29016e-03  -2.65160e-08
   2  p1           7.57130e+01   1.55891e+00   6.72214e-03   8.21832e-09
Info in : file graphtest4.png has been created
fitting result: const =  98.9861239576 , pitch =  75.7130326833