rf515_hfJSON.py

## \ingroup tutorial_roofit_main

## \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/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()