RubyROOT example: fill histogram then fit with gaussian+pol1

read_and_fit_histogram.rb

require "RubyROOT"
include Root
include RootApp

inputFile="histogram_sample.data"
outputPDFFile="histogram_sample.pdf"

#create an instance of histogram
hist=TH1D.create("hist","Histogram",512,0,512)

#read text data that contains counts of each histogram bin
open(inputFile).each_with_index(){|line,i|
	binIndex=hist.GetXaxis().FindBin(i)
	hist.SetBinContent(binIndex,line.to_i)
}


#draw with statistical error
canvas=TCanvas.create("c","Canvas",600,600)
hist.Draw("e")


#fit the 40K line
f_pol1_gaus=TF1.new("f_pol1_gaus","gaus(0)+pol1(3)",150,200)
f_pol1_gaus.SetParameter(0,200)
f_pol1_gaus.SetParameter(1,180)
f_pol1_gaus.SetParameter(2,10)
f_pol1_gaus.SetParameter(3,200)
f_pol1_gaus.SetParameter(4,-1)
f_pol1_gaus.SetLineColor(KOrange)
hist.Fit("f_pol1_gaus","","",150,200)

#save as pdf
hist.SaveAs(outputPDFFile)

#print fit statistics
puts "NDF  = #{f_pol1_gaus.GetNDF()}"
puts "Chi2 = #{"%.2f"%f_pol1_gaus.GetChisquare()}"

#run ROOT GUI event loop
canvas.Update
run_app

See http://ytkyk.info/blog/2015/06/22/rubyroot_example_fit_histogram/ for Japanese description of this example.