rf515_hfJSON.py

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## \file
## \ingroup tutorial_roofit
## \notebook
## Code HistFactory Models in JSON.
##
## With the HS3 standard, it is possible to code RooFit-Models of any kind as JSON files.
## In this tutorial, you can see how to code up a (simple) HistFactory-based model in JSON and import it into a RooWorkspace.
##
## \macro_code
##
## \date November 2021
## \author Carsten Burgard
 
import ROOT
 
# start by creating an empty workspace
ws = ROOT.RooWorkspace("workspace")
 
# the RooJSONFactoryWSTool is responsible for importing and exporting things to and from your workspace
tool = ROOT.RooJSONFactoryWSTool(ws)
 
# use it to import the information from your JSON file
tool.importJSON(ROOT.gROOT.GetTutorialDir().Data() + "/roofit/rf515_hfJSON.json")
ws.Print()
 
# now, you can easily use your workspace to run your fit (as you usually would)
# the model config is named after your pdf, i.e. <the pdf name>_modelConfig
model = ws["ModelConfig"]
 
# for resetting the parameters after the fit
params = model.GetPdf().getParameters(ws["observed"])
ROOT.SetOwnership(params, True)
params_initial = params.snapshot()
ROOT.SetOwnership(params_initial, True)
 
# we are fitting a clone of the model now,
result = model.fitTo(ws["observed"], ROOT.RooFit.Save(), ROOT.RooFit.PrintLevel(-1))
ROOT.SetOwnership(result, True)
result.Print()
# reset parameters, such that we are not double-fitting the model in the
# closure check.
params.assign(params_initial)
 
# in the end, you can again write to json
# the result will be not completely identical to the JSON file you used as an input, but it will work just the same
tool.exportJSON("myWorkspace.json")
 
# You can again import it if you want and check for closure
ws_2 = ROOT.RooWorkspace("workspace")
tool_2 = ROOT.RooJSONFactoryWSTool(ws_2)
tool_2.importJSON("myWorkspace.json")
ws_2.Print()
model_2 = ws_2["ModelConfig"]
result = model_2.fitTo(ws_2["observed"], ROOT.RooFit.Save(), ROOT.RooFit.PrintLevel(-1))
ROOT.SetOwnership(result, True)
result.Print()