# Rf 1 0 4_Classfactory¶

Basic functionality: the class factory for functions and pdfs

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.

Author: Clemens Lange, Wouter Verkerke (C++ version)
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Monday, January 17, 2022 at 09:50 AM.

In [ ]:
import ROOT


## Write class skeleton code¶

Write skeleton pdf 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+'
In [ ]:
ROOT.RooClassFactory.makePdf("MyPdfV1", "x,A,B")


## With added initial value expression¶

Write skeleton pdf class with variable x,a,b and given formula expression To use this class,

• Compile and link class with '.x MyPdfV2.cxx+'
In [ ]:
ROOT.RooClassFactory.makePdf("MyPdfV2", "x,A,B", "", "A*fabs(x)+pow(x-B,2)")


## With added analytical integral expression¶

Write skeleton pdf 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+'
In [ ]:
ROOT.RooClassFactory.makePdf(
"MyPdfV3",
"x,A,B",
"",
"A*fabs(x)+pow(x-B,2)",
True,
False,
"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

In [ ]:
ROOT.gROOT.ProcessLineSync(".x MyPdfV3.cxx+")


Creat instance of MyPdfV3 class

In [ ]:
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 pdf on frame

In [ ]:
frame1 = y.frame(Title="Compiled class MyPdfV3")
data = pdf.generate({y}, 1000)
pdf.fitTo(data)
data.plotOn(frame1)
pdf.plotOn(frame1)


/ Compiled version of example rf103# /

Declare observable x

In [ ]:
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

In [ ]:
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))))", [x, alpha])


Generate a toy dataset from the interpreted pdf

In [ ]:
data2 = genpdf.generate({x}, 50000)


Fit the interpreted pdf to the generated data

In [ ]:
genpdf.fitTo(data2)


Make a plot of the data and the pdf overlaid

In [ ]:
frame2 = x.frame(Title="Compiled version of pdf of rf103")
data2.plotOn(frame2)
genpdf.plotOn(frame2)


Draw all frames on a canvas

In [ ]:
c = ROOT.TCanvas("rf104_classfactory", "rf104_classfactory", 800, 400)
c.Divide(2)
c.cd(1)
frame1.GetYaxis().SetTitleOffset(1.4)
frame1.Draw()
c.cd(2)

from ROOT import gROOT