Re: Using Parameters in TTreeFormula's?

Robert,

As already explained, you have everything you want in TTree::UnbinnedFit. In the doc of this function, we give an example with one variable

//     TF1* f1 = new TF1("f1", "gaus(0)/sqrt(2*3.14159)/[2]", 0, 5);
//     f1->SetParameters(1, 3.1, 0.01);
//     f1->SetParLimits(0, 1, 1); // fix the normalization parameter to 1
//     data->UnbinnedFit("f1", "jpsimass", "jpsipt>3.0");

in case of 3 variables, give a TF3 as input using either an inline formula as above for the 1-d case
or a Double_t myfunc(Double_t*x, Double_t*par). and call UnbinnedFit with something like

       data->UnbinnedFit(myfunc,"var1:var2:var3","some condition") where var1, var2, var3 are the 3 ntuple variables that you want to fit.

Rene Brun
Robert Feuerbach wrote:
> Hi Philippe,
>
> Thank you for your indulgence, but from what I have seen in the
> examples and my understanding of using TF1, what UnbinnedFit does
> is fit a 'distribution' of events, not the relation between
> different variables in the tree. If I am wrong, please point me
> to an example of fitting the relation between two or more tree
> variables.
>
> For now, for my specialized case, if TTreeFormula's Parameters
> worked similarly to TFormula, I'm following the minexam.cxx
> example and using my own fcnk0( ) which has to be modified by
> hand for every case.
>
> As for an implementation of the 'Minimize' method/routine, it
> would be something like what is below.
>
> Take care,
> Rob Feuerbach
>
>
> ///////////////////////////////////////////////////////////////////
> // NON-WORKING CODE -- DO NOT USE !!!!
> //
> // Would be a general Minimize method for correlations between
> // tree variables BUT TTreeFormula's do not have working
> // parameters. Based on minexam.cxx
> // R.J. Feuerbach 2006
>
> // global variables to pass between fnck0 and Minimize
> TTreeFormula *express=0;
> TTree *tree=0;
>
> void fcnk0(int &, double *, double &f, double *x, int iflag) {
> f = 0;
> if (!tree || !express) return;
> express->SetParameters(x);
> Long64_t *lst = 0;
> Long64_t nev=tree->GetEntries();
> TEventList *ev = tree->GetEventList();
> if (ev) {
> lst = ev->GetList();
> nev = ev->GetN();
> }
> for (Long64_t i=0; i<nev; i++) {
> tree->GetEntry( (lst ? lst[i] : i ) );
> // assuming a 1-dimensional expression
> Double_t ex = express->EvalInstance();
> f += ex;
> }
> return;
> }
>
>
> Int_t Minimize(TTree *t, const char* varexp,
> const char *select, Double_t *parms) {
>
> {
> // take the expression 'varexp' and minimize it,
> // varying the listed parameters.
> // the parameters must be initialized.
> tree = t;
> express = new TTreeFormula("Expression",varexp,tree);
> express->SetParameters(parms);
>
> if (select && strlen(select)) {
> tree->Draw(">>elist",select);
> tree->SetEventList((TEventList*)gDirectory->Get("elist"));
> }
> // to speed things up, have only the needed branches on
> tree->SetBranchStatus("*",0);
> for (int i=0; i<express->GetNcodes(); i++) {
> TLeaf *lf = express->GetLeaf(i);
> if (lf) tree->SetBranchStatus(lf->GetBranch()->GetName(),1);
> }
>
> Int_t npar = express->GetNpar();
> TVirtualFitter *minuit = TVirtualFitter::Fitter(0,npar);
>
> minuit->SetFCN(fcnk0);
> for (int i=0; i<npar; i++) {
> minuit->SetParameter(i,Form("%d",i),parms[i],.1,0,0);
> }
> Double_t arglist[100];
> arglist[0]=0;
> minuit->ExecuteCommand("SET PRINT", arglist,1);
> minuit->ExecuteCommand("MIGRAD", arglist,0);
> for (int i=0; i<npar; i++) {
> parms[i] = minuit->GetParameter(i);
> }
> // clean up and turn all branches back on
> delete express;
> tree->SetBranchStatus("*",1);
> }
>
>
> // called as
> Double_t parms[2] = { .1, .1};
> Minimize(T,"(electronP-([0]*preshowerE+[1]*showerE))**2","",parms);
>
> ////////////
>
>
>
>
>
>
> On Wed, 11 Oct 2006, Philippe Canal wrote:
>
>
>> Date: Wed, 11 Oct 2006 15:56:08 -0500
>> From: Philippe Canal <pcanal_at_fnal.gov>
>> To: 'Robert Feuerbach' <feuerbac_at_jlab.org>, 'Rene Brun' <Rene.Brun_at_cern.ch>
>> Cc: roottalk_at_pcroot.cern.ch
>> Subject: RE: [ROOT] Using Parameters in TTreeFormula's?
>>
>> Hi Robert,
>>
>> What you are looking for really seems to be exactly TTree::UnbinnedFit.
>> Why is that function not appropriate?
>>
>>
>>> This is a very easy routine or method to write for the general case ...
>>>
>> Out of curiosity, what would it look like?
>>
>> Cheers,
>> Philippe.
>>
>
>
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Received on Thu Oct 12 2006 - 06:00:45 MEST