Re: ?: how to use TTreeFormula

Andy Haas (root_news@yahoo.com)
Mon, 31 Aug 1998 13:25:48 -0700 (PDT)

I believe you're out of luck. TTreeFormula is for making selections on
which events to draw, not as functions on the arguments themselves. In
order to do this, you need to fill the histogram manually, i.e.,

for (int i = 0; i<30000; i++) {
H1->Fill(Fun1(y),y);
}
H1->Draw();

The TTree::Draw() function is not intended for filling complicated
histograms, but quickly viewing a simple plot.

Cheers,
Andy

---Dirk Meier <Dirk.Meier@cern.ch> wrote:
>
>
>
> Hello,
>
> I want to draw a function TF1 which gets its arguments from a TTree.
>
> s.th like this:
>
> {
> TFile *f = new TFile("test.root"); // open file test.root
>
> TTree *t = (TTree*)f->Get("T"); // get the tree,
>
> TH1F *h1_1 = new TH1F("H1_1","H1_1",80,-0.1,1.1); // declare
histogramm
>
> T->Draw("x>>H1_1","y<1 && y>0","",30000); // Draw values from
> // tree into H1, x, y are floats in tree
>
>
> TF1 *fun1 = new TF1("Fun1","pol7",0,1); // decleare a function
>
> H1_1->Fit("Fun1","","",0,1); // do a fit to the
distribution of x
>
> // now I want to draw Fun1 as a function of y which is float in the
tree
>
> // s.th like T->Draw("Fun1(y):y","y<1 && y>0","",30000);
>
> }
>
>
> I believe TTreeFormula could help?
> Does anybody has an example on how to use TTreeFormula
>
>
> merci
>
> Dirk
>
>
>
>

==
Andrew Haas - haas@yahoo.com
University of Washingon Physics
Glast - D0

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