rf104_classfactory.py

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## \file
## \ingroup tutorial_roofit
## \notebook
## Basic functionality: the class factory for functions and p.d.f.s
##
## NOTE: This demo uses code that is generated by the macro,
##      which can be compiled on the fly (set to MyPdfV3 below).
##      To use MyPdfV1 or MyPdfV2, adjust lines below accordingly.
##
## \macro_code
##
## \date February 2018
## \author Clemens Lange, Wouter Verkerke (C++ version)

import ROOT

# Write class skeleton code
# --------------------------------------------------

# Write skeleton p.d.f class with variable x,a,b
# To use this class,
#    - Edit the file MyPdfV1.cxx and implement the evaluate() method in terms of x,a and b
#    - Compile and link class with '.x MyPdfV1.cxx+'
#
ROOT.RooClassFactory.makePdf("MyPdfV1", "x,A,B")

# With added initial value expression
# ---------------------------------------------------------------------

# Write skeleton p.d.f class with variable x,a,b and given formula expression
# To use this class,
#    - Compile and link class with '.x MyPdfV2.cxx+'
#
ROOT.RooClassFactory.makePdf(
    "MyPdfV2", "x,A,B", "", "A*fabs(x)+pow(x-B,2)")

# With added analytical integral expression
# ---------------------------------------------------------------------------------

# Write skeleton p.d.f class with variable x,a,b, given formula expression _and_
# given expression for analytical integral over x
# To use this class,
#    - Compile and link class with '.x MyPdfV3.cxx+'
#
ROOT.RooClassFactory.makePdf(
    "MyPdfV3",
    "x,A,B",
    "",
    "A*fabs(x)+pow(x-B,2)",
    ROOT.kTRUE,
    ROOT.kFALSE,
    "x:(A/2)*(pow(x.max(rangeName),2)+pow(x.min(rangeName),2))+(1./3)*(pow(x.max(rangeName)-B,3)-pow(x.min(rangeName)-B,3))")

# Use instance of created class
# ---------------------------------------------------------

# Compile MyPdfV3 class
ROOT.gROOT.ProcessLineSync(".x MyPdfV3.cxx+")

# Creat instance of MyPdfV3 class
a = ROOT.RooRealVar("a", "a", 1)
b = ROOT.RooRealVar("b", "b", 2, -10, 10)
y = ROOT.RooRealVar("y", "y", -10, 10)
pdf = ROOT.MyPdfV3("pdf", "pdf", y, a, b)

# Generate toy data from pdf and plot data and p.d.f on frame
frame1 = y.frame(ROOT.RooFit.Title("Compiled class MyPdfV3"))
data = pdf.generate(ROOT.RooArgSet(y), 1000)
pdf.fitTo(data)
data.plotOn(frame1)
pdf.plotOn(frame1)

# /
# C o m p i l e d   v e r s i o n   o f   e x a m p l e   r f 1 0 3 #
# /

# Declare observable x
x = ROOT.RooRealVar("x", "x", -20, 20)

# The ROOT.RooClassFactory.makePdfInstance() function performs code writing, compiling, linking
# and object instantiation in one go and can serve as a straight
# replacement of ROOT.RooGenericPdf

alpha = ROOT.RooRealVar("alpha", "alpha", 5, 0.1, 10)
genpdf = ROOT.RooClassFactory.makePdfInstance(
    "GenPdf",
    "(1+0.1*fabs(x)+sin(sqrt(fabs(x*alpha+0.1))))",
    ROOT.RooArgList(
        x,
        alpha))

# Generate a toy dataset from the interpreted p.d.f
data2 = genpdf.generate(ROOT.RooArgSet(x), 50000)

# Fit the interpreted p.d.f to the generated data
genpdf.fitTo(data2)

# Make a plot of the data and the p.d.f overlaid
frame2 = x.frame(ROOT.RooFit.Title("Compiled version of pdf of rf103"))
data2.plotOn(frame2)
genpdf.plotOn(frame2)

# Draw all frames on a canvas
c = ROOT.TCanvas("rf104_classfactory", "rf104_classfactory", 800, 400)
c.Divide(2)
c.cd(1)
ROOT.gPad.SetLeftMargin(0.15)
frame1.GetYaxis().SetTitleOffset(1.4)
frame1.Draw()
c.cd(2)
ROOT.gPad.SetLeftMargin(0.15)
frame2.GetYaxis().SetTitleOffset(1.4)
frame2.Draw()

c.SaveAs("rf104_classfactory.png")