rf502_wspacewrite.py

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## \file
## \ingroup tutorial_roofit
## \notebook -nodraw
##
## Organization and simultaneous fits: creating and writing a workspace
##
## \macro_code
##
## \date February 2018
## \author Clemens Lange, Wouter Verkerke (C++ version)

import ROOT


# Create model and dataset
# -----------------------------------------------

# Declare observable x
x = ROOT.RooRealVar("x", "x", 0, 10)

# Create two Gaussian PDFs g1(x,mean1,sigma) anf g2(x,mean2,sigma) and
# their parameters
mean = ROOT.RooRealVar("mean", "mean of gaussians", 5, 0, 10)
sigma1 = ROOT.RooRealVar("sigma1", "width of gaussians", 0.5)
sigma2 = ROOT.RooRealVar("sigma2", "width of gaussians", 1)

sig1 = ROOT.RooGaussian("sig1", "Signal component 1", x, mean, sigma1)
sig2 = ROOT.RooGaussian("sig2", "Signal component 2", x, mean, sigma2)

# Build Chebychev polynomial p.d.f.
a0 = ROOT.RooRealVar("a0", "a0", 0.5, 0., 1.)
a1 = ROOT.RooRealVar("a1", "a1", -0.2, 0., 1.)
bkg = ROOT.RooChebychev("bkg", "Background", x, ROOT.RooArgList(a0, a1))

# Sum the signal components into a composite signal p.d.f.
sig1frac = ROOT.RooRealVar(
    "sig1frac", "fraction of component 1 in signal", 0.8, 0., 1.)
sig = ROOT.RooAddPdf(
    "sig", "Signal", ROOT.RooArgList(sig1, sig2), ROOT.RooArgList(sig1frac))

# Sum the composite signal and background
bkgfrac = ROOT.RooRealVar("bkgfrac", "fraction of background", 0.5, 0., 1.)
model = ROOT.RooAddPdf(
    "model", "g1+g2+a", ROOT.RooArgList(bkg, sig), ROOT.RooArgList(bkgfrac))

# Generate a data sample of 1000 events in x from model
data = model.generate(ROOT.RooArgSet(x), 1000)

# Create workspace, import data and model
# -----------------------------------------------------------------------------

# Create a empty workspace
w = ROOT.RooWorkspace("w", "workspace")

# Import model and all its components into the workspace
getattr(w, 'import')(model)

# Import data into the workspace
getattr(w, 'import')(data)

# Print workspace contents
w.Print()

# Save workspace in file
# -------------------------------------------

# Save the workspace into a ROOT file
w.writeToFile("rf502_workspace.root")