RooFit in Python

[wamorkar.t]

Dear experts,

I am trying to write a code that has multiple pdf’s and want to be able to fit them to data and plot the background model along with plot. Including the appropriate snippet:

    w = ROOT.RooWorkspace("w")
    # create the variable
    w.factory( "tp_mass[100, 160]" )
    w.var( "tp_mass" ).SetTitle("tp_mass")
    w.var( "tp_mass" ).setUnit("GeV")

    w.factory( "dp1_mass[0,200]" )
    w.factory( "dp2_mass[0,200]" )

    # the set of variables
    treeVars = ROOT.RooArgSet()
    treeVars.add( w.var( "tp_mass" ) )
    treeVars.add( w.var("dp1_mass") )
    treeVars.add( w.var("dp2_mass") )
    data_RooDataSet = ROOT.RooDataSet( "data", "data", ROOT.RooArgSet( w.var( "tp_mass" ) ) )

    #RooArgList *mypdfs
    for itree in range(len(trees_data['trees'])) :

      data_RooDataSet_temp = ROOT.RooDataSet( "data", "data", (trees_data['trees'][itree]), treeVars)
      data_RooDataSet.append(data_RooDataSet_temp.reduce('(' + trees_data['weights'][itree] + ') * (' + cuts[cutName] + ')'))
      c1 = TCanvas('c1','PDF Fits',200,10,700,500)
      frame = tp_mass.frame()
      data.plotOn(frame)

However this throws me the error
"data.plotOn(frame)
AttributeError: ‘str’ object has no attribute ‘plotOn’"

I am using RooFit with python. Any help is very appreciated.

[amadio]

I do not see where you created the data Python object. Python is assuming it is a string, which does not have the method for plotting. Maybe you meant data_RooDataSet.plotOn(frame)?

[wamorkar.t]

Thanks for your reply Guilherme.
Maybe I should have specified, but I do create the RooDataSet called “data”

@wamorkar.t

data_RooDataSet = ROOT.RooDataSet( “data”, “data”, ROOT.RooArgSet( w.var( “tp_mass” ) ) )

Is that not the correct syntax for creating “data” ?

Thanks in advance,
Tanvi

[wamorkar.t]

I spoke too soon. Your solution worked. Thanks a lot!

[wamorkar.t]

Hi Guilherme,

I have a related question:
I created some pdf’s and now want to plot the bkg_exp_pdf

    w.factory( "Exponential:bkg_exp_pdf(tp_mass, a1[4.03336e-02, 0.0001, 10])")
    w.factory( "Exponential:bkg_exp2_pdf(tp_mass, a2[4.88218e-01, 0.0001, 10])")
    w.factory( "Exponential:bkg_pdf(tp_mass, a[-0.5,-2,-0.2])"  )

    c1 = TCanvas('c1','PDF Fits',200,10,700,500)
    frame = tp_mass.frame()
    bkg_exp_pdf.plotOn(frame)

But get the error:
"NameError: name ‘bkg_exp_pdf’ is not defined"
Can you point my mistake here?

Many thanks in advance,
Tanvi

[amadio]

Sure, when you call

w.factory( "Exponential:bkg_exp_pdf(tp_mass, a1[4.03336e-02, 0.0001, 10])")

you still need a way to get a hold of the Python object later, as it’s not created automatically

# not quite sure if this is what you want, but something similar to what's below
bkg_exp_pdf = ROOT.RooDataSet( "bkg_exp_pdf", "bkg_exp_pdf", ROOT.RooArgSet( w.var( "tp_mass" ) ) )
bkg_exp_pdf.plotOn(frame)

That is, the name given to the factory does not create the Python object by itself, you have to create it.
That is also why you needed data_RooDataSet before instead of just data, since Python didn’t know about the object named data, since you had created it with the other name. Hope that helps.

[wamorkar.t]

Thanks Guilherme for all the help