Rf 2 0 7_Comptools¶

'ADDITION AND CONVOLUTION' RooFit tutorial macro #207 Tools and utilities for manipulation of composite objects

Author: Wouter Verkerke (C version)
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Wednesday, January 19, 2022 at 10:14 AM.

In [ ]:
import ROOT

Set up composite pdf dataset¶

Declare observable x

In [ ]:
x = ROOT.RooRealVar("x", "x", 0, 10)

Create two Gaussian PDFs g1(x,mean1,sigma) anf g2(x,mean2,sigma) and their parameters

In [ ]:
mean = ROOT.RooRealVar("mean", "mean of gaussians", 5)
sigma = ROOT.RooRealVar("sigma", "width of gaussians", 0.5)
sig = ROOT.RooGaussian("sig", "Signal component 1", x, mean, sigma)

Build Chebychev polynomial p.d.f.

In [ ]:
a0 = ROOT.RooRealVar("a0", "a0", 0.5, 0.0, 1.0)
a1 = ROOT.RooRealVar("a1", "a1", 0.2, 0.0, 1.0)
bkg1 = ROOT.RooChebychev("bkg1", "Background 1", x, [a0, a1])

Build expontential pdf

In [ ]:
alpha = ROOT.RooRealVar("alpha", "alpha", -1)
bkg2 = ROOT.RooExponential("bkg2", "Background 2", x, alpha)

Sum the background components into a composite background p.d.f.

In [ ]:
bkg1frac = ROOT.RooRealVar("bkg1frac", "fraction of component 1 in background", 0.2, 0.0, 1.0)
bkg = ROOT.RooAddPdf("bkg", "Signal", [bkg1, bkg2], [bkg1frac])

Sum the composite signal and background

In [ ]:
bkgfrac = ROOT.RooRealVar("bkgfrac", "fraction of background", 0.5, 0.0, 1.0)
model = ROOT.RooAddPdf("model", "g1+g2+a", [bkg, sig], [bkgfrac])

Create dummy dataset that has more observables than the above pdf

In [ ]:
y = ROOT.RooRealVar("y", "y", -10, 10)
data = ROOT.RooDataSet("data", "data", {x, y})

Get list of observables¶

Get list of observables of pdf in context of a dataset

Observables are define each context as the variables shared between a model and a dataset. In self case that is the variable 'x'

In [ ]:
model_obs = model.getObservables(data)
model_obs.Print("v")

Get list of parameters¶

Get list of parameters, list of observables

In [ ]:
model_params = model.getParameters({x})
model_params.Print("v")

Get list of parameters, a dataset (Gives identical results to operation above)

In [ ]:
model_params2 = model.getParameters(data)
model_params2.Print()

Get list of components¶

Get list of component objects, top-level node

In [ ]:
model_comps = model.getComponents()
model_comps.Print("v")

Modifications to structure of composites¶

Create a second Gaussian

In [ ]:
sigma2 = ROOT.RooRealVar("sigma2", "width of gaussians", 1)
sig2 = ROOT.RooGaussian("sig2", "Signal component 1", x, mean, sigma2)

Create a sum of the original Gaussian plus the second Gaussian

In [ ]:
sig1frac = ROOT.RooRealVar("sig1frac", "fraction of component 1 in signal", 0.8, 0.0, 1.0)
sigsum = ROOT.RooAddPdf("sigsum", "sig+sig2", [sig, sig2], [sig1frac])

Construct a customizer utility to customize model

In [ ]:
cust = ROOT.RooCustomizer(model, "cust")

Instruct the customizer to replace node 'sig' with node 'sigsum'

In [ ]:
cust.replaceArg(sig, sigsum)

Build a clone of the input pdf according to the above customization instructions. Each node that requires modified is clone so that the original pdf remained untouched. The name of each cloned node is that of the original node suffixed by the name of the customizer object

The returned head node own all nodes that were cloned as part of the build process so when cust_clone is deleted so will all other nodes that were created in the process.

In [ ]:
cust_clone = cust.build(ROOT.kTRUE)

Print structure of clone of model with sig.sigsum replacement.

In [ ]:
cust_clone.Print("t")

The RooCustomizer has the be deleted first. Otherwise, it might happen that sig or sigsum are deleted first, in which case the internal TLists in the RooCustomizer will complain about deleted objects.

In [ ]:
del cust

Draw all canvases

In [ ]:
from ROOT import gROOT
gROOT.GetListOfCanvases().Draw()