Roofit and PyROot

ROOT
1

Hello

I’m trying some basic stuff with Roofit through PyRoot.

>>> hh=TH1F("hh", "test histo", 100, -5, 5)
>>> hh.FillRandom("gaus", 10000)
>>> hh.Draw()
>>> x=RooRealVar("x", "x", -5, 5)

RooFit v2.10 -- Developed by Wouter Verkerke and David Kirkby 
                Copyright (C) 2000-2005 NIKHEF, University of California & Stanford University
                All rights reserved, please read http://roofit.sourceforge.net/license.txt

>>> data=RooDataHist("data", "dataset with x", x, hh)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: none of the 5 overloaded methods succeeded. Full details:
  RooDataHist::RooDataHist() =>
    takes at most 0 arguments (4 given)
  RooDataHist::RooDataHist(const char* name, const char* title, const RooArgSet& vars) =>
    takes at most 3 arguments (4 given)
  RooDataHist::RooDataHist(const RooDataHist& other, const char* newname = 0) =>
    takes at most 2 arguments (4 given)
  RooDataHist::RooDataHist(const char* name, const char* title, const RooArgSet& vars, const RooAbsData& data, Double_t initWgt = 1.0) =>
    could not convert argument 3
  RooDataHist::RooDataHist(const char* name, const char* title, const RooArgList& vars, const TH1* hist, Double_t initWgt = 1.0) =>
    could not convert argument 3

Equivalent code in bare root works but apparently there’s some problem with type, I proceeded as follows,

>>> data=RooDataHist("data", "dataset with x", RooArgList(x), hh)
>>> frame=x.frame()
>>> data.plotOn(frame)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: RooPlot* RooDataHist(RooPlot* frame, RooTreeData::PlotOpt o) =>
    takes at least 2 arguments (1 given)

at this point I don’t really know what to do… Could you tell me where I’m doing wrong?

Cheers
Akira

2

Akira,

not an expert on RooFit myself, but the error says that the constructor will accept a RooArgList or RooArgSet as the third argument, but not just a RooRealVar. Hence, I’d argue that this would be the way to go:[code]>>> l = RooArgList(x)

data=RooDataHist(“data”, “dataset with x”, l, hh)[/code]

(See help(RooArgList) for its available constructors.) Presumably, you took the code from a C++ example? There I’d expect that the RooRealVar can be implicitly converted to a RooArgList, which can be passed through the const-ref. Allowing implicit conversions in PyROOT (something that has no equivalent in the python language) has been on my TODO list for a long time. :slight_smile:

HTH,
Wim

3

Hi Wim

OK, that explains the first part of my problem. In the second bit of my code, though, I have actually tried that and I managed to go pass that line. Then I’m trying to plot it on a frame and get "takes at least 2 arguments (1 given) " error. The problem is that this is an internal error and I have no way of passing this missing argument from plotOn() method. I guess this may be more of a RooFit issue but this problem is specific to using pyRoot as the same (equivalent) thing works on CINT.

Cheers
Akira

4

Akira,

not sure how you think it’s an internal error (then again, the error message is misleading: it is missing “::plotOn”; there’s one ROOT release out there that suffers from this). Here, too, the C++ version is using a feature that isn’t readily ported to python, in this case “using RooAbsData::plotOn”. The line, therefore, should be replaced by a direct call to the function in that base class:>>> RooAbsData.plotOn(data,frame)Clumsy, yes, but I don’t know anything better. :frowning:

Cheers,
Wim