RooPolyVar.x() yields a default variable Name of "x"

[Phmonski]

Check duplicate issues.

• Checked for duplicates

Description

When running RooPolyVar().x(), the proxy has a default name of "x" despite different variable name.

Reproducer

import ROOT

y = ROOT.RooRealVar("y", "y", 1, -5, 5)

a = ROOT.RooRealVar("a", "a", 2, -5, 5)
b = ROOT.RooRealVar("b", "b", 3, -5, 5)

func = ROOT.RooPolyVar("myFunc", "myFunc", y, [a, b])
func.Print("t")
print("Function Variable:", func.x().GetName())

ROOT version

6.37.01

Installation method

build from source

Operating system

ArchLinux

Additional context

No response

[ferdymercury]

I guess this is not restricted to RooPolyVar, but to many other functions in RooFit, where the convention is that the name of the dependent variable is simply "x" no matter what the roorealvar variable name/title is.

RooPolyVar
RooRangeBoolean
RooExponential
RooChiSquarePdf
RooCrystalBall
RooParametricStepFunction
RooStepFunction
RooVoigtian
RooBreitWigner
RooBifurGauss
RooLandau
RooLegacyExpPoly
RooBernstein
RooCBShape
RooPowerSum
RooChebychev
RooPolynomial

[guitargeek]

Thanks for the report! Indeed, as @ferdymercury said, the proxy that a RooFit object like a RooExponential holds to wrap the actual input has a hardcoded name.

But these getters like RooPolyVar::x() should return the underlying RooAbsReal, and not the proxy. That's what was wrong in this case, and the bug report is very valid.

I have opened a PR with the fix:

• [RF] Return reference to actual RooAbsReal in RooPolyVar::x() getter #20442