2D histogram fitted with rooEllipse

Roofit and RooStats
1

Dear rooFitter,

I have some problems with my code and I hope you can help me…

I’d like to fit a 2D Chi2 distribution (it’s a 2D histogram and the distribution is an ellipse). To do that I tried many things and I have finally chosen rooEllipse but unlike to what I have think, I can’t find the solution.

My 2D histogram is named hChi2. First I have tried to import and plot the 2D histogram in rooEllipse with different technics:

  1. RooRealVar x(“x”,“x”,-0.5,60.5);
    RooRealVar y(“y”,“y”,-0.5,49.5);
    RooDataHist* roohChi2 = new RooDataHist(“roohChi2”,“hChi2 import”,RooArgSet(x,y), Import(*hChi2));

    RooPlot* frame = new RooPlot(-0.5,60.5,-0.5,49.5) ;
    roohChi2->plotOn(frame);
    frame->Draw();

  2. RooAbsData* data;
    TH2* roohChi2 = x.createHistogram(“Chi2 dans roofit”, y,0,0,0,10000);
    data->fillHistogram(roohChi2, RooArgList(x,y));
    data->Draw();

PROBLEMS :

  • with test 1) : The compilation is OK but I have problems in execution and an empty plot
    [#1] INFO:DataHandling – RooDataHist::adjustBinning(roohChi2): fit range of variable x expanded to nearest bin boundaries: [-0.5,60.5] --> [-0.5,60.5]
    [#1] INFO:DataHandling – RooDataHist::adjustBinning(roohChi2): fit range of variable y expanded to nearest bin boundaries: [-0.5,49.5] --> [-0.5,49.5]
    [#1] INFO:InputArguments – RooAbsData::plotOn(roohChi2) INFO: dataset has non-integer weights, auto-selecting SumW2 errors instead of Poisson errors
    [#0] ERROR:InputArguments – RooDataHist::roohChi2:plotOn: frame does not specify a plot variable

  • with test 2) : The compilation fails with error :
    error: initializing argument 6 of ‘TH2F* RooAbsRealLValue::createHistogram(const char*, const RooAbsRealLValue&, const char*, Double_t*, Double_t*, Int_t*) const’ [-fpermissive]
    TH2F *createHistogram(const char *name, const RooAbsRealLValue &yvar, const char *zAxisLabel=0,

For the frame I have also tested :

  1. RooPlot *frame = x.frame();
    roohChi2->plotOn(frame);
    roohChi2->Draw(“LEGO”);

  2. RooPlot* yframe = y.frame(Bins(40),Title(" ")) ;
    roohChi2->plotOn(yframe) ;

Neither give good results…

After this 2D histogram import, I’d like to fit with rooEllipse. I plan to use :
RooEllipse contour(“contour”, “contour”, 50.0, 20.0, 0.01, 0.01, 0.85);
contour.fitTo(rooHisto) ;
contour.plotOn(frame) ;

I have also seen on the Internet :
RooEllipse *contour= new RooEllipse(“contour”,50.0, 20.0, 0.01, 0.01, 0.85);
frame->addPlotable(contour);

Do you know the right solution?

I begin in ROOT and rooFit, if you have any idea I’ll take it !

Thank to read me :wink:
M.

2

Hi,

perhaps a good starting point is this tutorial: root.cern.ch/doc/master/fitCircle_8C.html
I would leave RooFit out of the equation.

Danilo

3

Hi Danilo !

Thank for answering ! :slight_smile:

You’re absolutly right Roofit is useless here because I’d like to minimized my distribution
I tried to change my code with your example and :
homepages.physik.uni-muenchen.de … ontour.cxx

These two methods used TMinuit and TVirtualFitter respectively but none of them give something. I have for both of these methods an execution error (the same):

*** Break *** segmentation violation

There was a crash.
This is the entire stack trace of all threads:

#0 0x00007fe493e56b4c in __libc_waitpid (pid=3703, stat_loc=stat_loc
entry=0x7ffdf7ac4f40, options=options
entry=0) at …/sysdeps/unix/sysv/linux/waitpid.c:31
#1 0x00007fe493ddc2e2 in do_system (line=) at …/sysdeps/posix/system.c:148
#2 0x00007fe494b5be43 in TUnixSystem::StackTrace() () from /home/m/root/lib/libCore.so
#3 0x00007fe494b5e68c in TUnixSystem::DispatchSignals(ESignals) () from /home/m/root/lib/libCore.so
#4
#5 0x00007fe4893794ff in TPad::PaintPolyLine(int, double*, double*, char const*) () from /home/m/root/lib/libGpad.so
#6 0x00007fe485a5b304 in ?? ()
#7 0x00007fe494e55670 in vtable for TString () from /home/m/root/lib/libCore.so
#8 0x0000000000000000 in ?? ()

The lines below might hint at the cause of the crash.
If they do not help you then please submit a bug report at
root.cern.ch/bugs. Please post the ENTIRE stack trace
from above as an attachment in addition to anything else
that might help us fixing this issue.

#5 0x00007fe4893794ff in TPad::PaintPolyLine(int, double*, double*, char const*) () from /home/m/root/lib/libGpad.so
#6 0x00007fe485a5b304 in ?? ()
#7 0x00007fe494e55670 in vtable for TString () from /home/m/root/lib/libCore.so
#8 0x0000000000000000 in ?? ()

I searched on the Internet a mean to fix this error but I did not find anything…
I put my code in attachment, maybe it’s a stupid error :blush: .

M.
my2dplot.root (63.9 KB)
my_test.C (4.85 KB)

4

I have tried your macro with ROOT 6 and ROOT 5.34.
It crashes with ROOT 6 but not with ROOT 5.34.
I will tell our fitting expert to have a look.

5

Hi Couet !

Thank a lot ! :slight_smile:
It’s a really strange behaviour…

Thank,
M.

6

Hi,

I can reproduce the issue with 6.06 on lxplus.
The full stack with debugging symbols is the following:

#0  0x00007ffff62168d2 in TPad::PaintPolyLine(int, double*, double*, char const*) () from /afs/cern.ch/sw/lcg/app/releases/ROOT/6.06.04/x86_64-slc6-gcc49-opt/root/lib/libGpad.so
#1  0x0000000000401fca in fcn(int&, double*, double&, double*, int) () at my_test.C:54
#2  0x00007fffe6f17197 in TMinuit::Eval(int, double*, double&, double*, int) () from /afs/cern.ch/sw/lcg/app/releases/ROOT/6.06.04/x86_64-slc6-gcc49-opt/root/lib/libMinuit.so
#3  0x00007fffe6f184fe in TMinuit::mnamin() () from /afs/cern.ch/sw/lcg/app/releases/ROOT/6.06.04/x86_64-slc6-gcc49-opt/root/lib/libMinuit.so
#4  0x00007fffe6f1b90f in TMinuit::mnmigr() () from /afs/cern.ch/sw/lcg/app/releases/ROOT/6.06.04/x86_64-slc6-gcc49-opt/root/lib/libMinuit.so
#5  0x00007fffe6f2c9e1 in TMinuit::mnexcm(char const*, double*, int, int&) () from /afs/cern.ch/sw/lcg/app/releases/ROOT/6.06.04/x86_64-slc6-gcc49-opt/root/lib/libMinuit.so
#6  0x00007fffe6f37cbd in TFitter::ExecuteCommand(char const*, double*, int) () from /afs/cern.ch/sw/lcg/app/releases/ROOT/6.06.04/x86_64-slc6-gcc49-opt/root/lib/libMinuit.so
#7  0x00000000004022d2 in my_test(double) () at my_test.C:91
#8  0x00000000004025ab in main () at my_test.C:115

This seems related to a painting of a line which happens within the function to minimise (fcn).

Cheers,
Danilo

7

The code is quite fragile.
If you remove the commented part of the macro it crashes in Eval instead in PaintPolyLine…
There is surely some memory overwriting …

8

Thanks both of you !

Danilo, I have the same issues… I tried to fix the problems but I don’t really find a solution…

Couet, you’re right my code is maybe quite fragile… this is my first code with TMinuit (and minmization in general) and it’s a little difficult :blush:

Cheers,
M.

9

Lorenzo found the issue … you are casting a TCanvas to an histogram:

    h2 = (TH2F*)f->Get("c1");
10

:slight_smile: That is indeed fatal!

11

Attached a new version your macro. Note that I commented out the ellipse drawing because it has wrong coordinates and obscures completely the histogram.
my_test.C (3.09 KB)

12

Thanks !!! =D> =D> =D> =D> =D>

It’s fatal indeed !

Cheers,
M.