Problem with fitting

ROOT
1

Hi.
I am using ROOT to fit some data. One of the sets of data is only of 4 entries, as shown in the code below:
x =-0.011079 time =0.00358523
x =-0.020798 time =0.00713421
x =-0.0293905 time =0.0106832
x =-0.0379928 time =0.0142322

Fitting results:
Error in <TDecompChol>: matrix not positive definite
Error in <TVectorD>: vectors not compatible
Fitting results:
Parameters:
NO.             VALUE           ERROR
0       0.000000        0.000000
1       0.000000        0.000000

The code I used for fitting is as follows:

gSystem->Load("libpdbd.so");

TFile* f = new TFile("output.root");

TTree* t =  (TTree*) f->Get("DBDmc");

Int_t NTracks, NTracksbefore;
Double_t x, y, z;
Float_t ener,time;
// Double_t x;

TLeaf* l_NTracks = t->GetLeaf("fNTracks");
TLeaf* l_fX = t->GetLeaf("fTracks.fX.fX");
TLeaf* l_fY = t->GetLeaf("fTracks.fX.fY");
TLeaf* l_fZ = t->GetLeaf("fTracks.fX.fZ");
TLeaf* l_fEnergy = t->GetLeaf("fTracks.fEnergy");
TLeaf* l_fTime = t->GetLeaf("fTracks.fTime");

NTracksbefore = 0;
Int_t nentries = (Int_t) t->GetEntries();
for (Int_t i=0; i<nentries>GetBranch()->GetEntry(i);
    NTracks = l_NTracks->GetValue();
    l_fX->GetBranch()->GetEntry(i);
    l_fY->GetBranch()->GetEntry(i);
    l_fZ->GetBranch()->GetEntry(i);
    l_fTime->GetBranch()->GetEntry(i);
    l_fEnergy->GetBranch()->GetEntry(i);
    
    // create profiles to hold the data
    TProfile* pr1 = new TProfile("pr1","x vs time", 100, 0, 2, -20, 20);
    TProfile* pr2 = new TProfile("pr2","y vs time", 100, 0, 2, -20, 20);
    TProfile* pr3 = new TProfile("h3","y and time", 100, 0, 2, -20, 20);
    for (Int_t j = NTracksbefore;j<NTracks>GetValue(j);
      y = l_fY->GetValue(j);
      z = l_fZ->GetValue(j);
      ener = l_fEnergy->GetValue(j);
      time = l_fTime->GetValue(j);
      pr1->Fill(time,x);
      pr2->Fill(time,y);
      pr3->Fill(time,z);
      cout << "x =" << x << "time =" << time <<endl>Fit("pol1");
    
    delete pr1;
    delete pr2;
    delete pr3;
    }

Is it an implicit problem in the ROOT fitter?
Thanks
Hui

2

hard to say, x is not assigned a value at all. Could you simplify code so one can test it (without any special libraries and trees) ?

3

Part of your code was removed by the HTML processor of the forum.
Could you please repost your code (and disable HTML in that post) and send it as attachement.

Thanks,
Philippe.