Hi Jeff -
you filled your tree not with the 4-vectors but with the simple doubles.
This is why you can't use methods of the 4-vectors - there is none of them
in the tree...
It is true that some of the KUIP commands are shorter than C++ statements -
this is always the case when you compare a command language and a programming
language. Yes, attaching the file takes less keyboard hits with PAW than with
ROOT. Keep in mind that one starts seeing the real advantages of ROOT only when
you come to more complicated analysis-oriented things: having interpreted
language being the same as the compiled language starts paying off only at
that stage and it really is a great deal.
I'd strongly suggest you to go through the ROOT HowTo's and Tutorials - if you
know Python and are used to SWIG it should be quite easy for you to figure how
to use ROOT/CINT properly. Also: let's keep the level of emotions on this list
low...
best, Pasha
Jeff Templon wrote:
>
> Hi,
>
> OK, so I am trying to use ROOT (I thought it would be easier than
> writing a Python wrapper for ROOT trees ... turns out I was right,
> keep reading ...).
>
> I wrote a macro which ran the very first time (!) which is supposed to
> generate a tree full of simulated J/psi electroproduction events.
> Each event will contain four TLorentzVector objects. This apparently
> happened as far as I can tell.
>
> Pain #1 - reattaching the Tree in the ROOT file seems to be much more
> complex than hi/fil 1 charm.root was
>
> Pain #2 - I don't see an easy way to go thru the entire Tree and plot
> say the magnitudes of the four-momenta (I thought the tree was
> supposed to keep all the object code intact which is why we were using
> C++ ... oh dear).
>
> TFile f("charm.root");
> TTree *mytree = (TTree*)f.Get("T"); // what a contorted command
> mytree.Draw("ppsi.fY"); // yields some error
> Error in <TCanvas::Range>: illegal world coordinates range: x1=13.684271, y1=-0.131250, x2=-1.520475, y2=1.181250
> Error in <TCanvas::RangeAxis>: illegal axis coordinates range: xmin=12.163796, ymin=0.000000, xmax=-0.000000, ymax=1.050000
> mytree.Draw("ppsi.fZ")
> Error in <TCanvas::Range>: illegal world coordinates range: x1=13.684271, y1=-0.393750, x2=-1.520475, y2=3.543750
> Error in <TCanvas::RangeAxis>: illegal axis coordinates range: xmin=12.163796, ymin=0.000000, xmax=-0.000000, ymax=3.150000
> mytree.Draw("ppsi.Mag()")
>
> *ERROR 26 :
> Unknown name : "ppsi.Mag()"
> Error in <TCanvas::Range>: illegal world coordinates range: x1=13.684271, y1=-0.393750, x2=-1.520475, y2=3.543750
> Error in <TCanvas::RangeAxis>: illegal axis coordinates range: xmin=12.163796, ymin=0.000000, xmax=-0.000000, ymax=3.150000
>
> ppsi.Mag() is the biggest disappointment. What is the use of having
> all these objects in the tree if I can't use their methods?
>
> Pain #3 - wading thru the documentation gives me no clue of how to do
> what I want to do, except for possibly the contorted, non-simple
> method shown under "The General Way" on URL
>
> http://root.cern.ch/root/HowtoReadTree.html
>
> Say it ain't so!!! Isn't OO supposed to make my life easier?
>
> JT
>
> ps In the very possible case that I have already blown it in my macro,
> here it is.
>
> // #-> charm.py -- simulate j/psi electroproduction at JLab
> // c++ version i hope
>
> // from Numeric import * [ left over from python version ]
> // from vec4 import *
> // import RNG
>
> // #-> simulation driver parameters
>
> main(int argc, char **argv)
> {
> float mj = 3096.88; // # J/psi mass in MeV
> float me = 0.510999; // # electron mass
> float mp = 938.272;
>
> float beamen = 11.0 * 1000.0; // # GeV * 1000 MeV/GeV
>
> float ll_the = (3.1415926 / 180) * 1.0; // last number is e- angle LL in deg
> float ul_the = (3.1415926 / 180) * 20.0; // last number is e- angle UL in deg
>
> // above is stored in radians since we will need to take cosines
> // below is not
>
> float ll_phe = -93.0; // LL on e- azimuthal angle (degrees now)
> float ul_phe = -87.0;
>
> float ll_pe = 2275; // LL on scat electron momentum (MeV/c)
> float ul_pe = 2780;
>
> int howmany = 10000; // # desired number of events
>
> // #-> set up random generators for electron. strategy: create sample
> // #-> arrays at start of program, just take values from them during
> // #-> execution
>
> TF1 *thegen = new TF1("thegen","sin(x)",ll_the,ul_the);
> TF1 *phegen = new TF1("phegen","1.0", ll_phe,ul_phe);
> TF1 *pegen = new TF1("pegen", "1.0", ll_pe, ul_pe );
>
> // #-> set up four-momenta for beam and target, which should not change
>
> TLorentzVector beam; beam.SetVectM(TVector3(0,0,beamen),me);
> TLorentzVector targ(0.0,0.0,0.0,mp);
>
> TFile hfile("charm.root","RECREATE","Charm");
>
> TTree *tree = new TTree("T","Charm Electroproduction");
>
> int nev = 0;
> TLorentzVector scat(1,1,1,1);
> TLorentzVector X;
>
> tree->Branch("beam",&beam,"fX/D:fY/D:fZ/D:fE/D");
> tree->Branch("targ",&targ,"fX/D:fY/D:fZ/D:fE/D");
> tree->Branch("scat",&scat,"fX/D:fY/D:fZ/D:fE/D");
> tree->Branch("ppsi",&X,"fX/D:fY/D:fZ/D:fE/D");
>
> for ( int nev = 1; nev <= howmany; nev++) {
> float thtmp = thegen.GetRandom();
> float phtmp = phegen.GetRandom();
> float ptmp = pegen.GetRandom();
>
> scat.SetVectM(TVector3(ptmp*sin(thtmp)*cos(phtmp),
> ptmp*sin(thtmp)*sin(phtmp),
> ptmp*cos(thtmp)),
> me);
>
> X = beam + targ - scat;
>
> tree->Fill();
> }
>
> hfile.Write();
> hfile.Close();
>
> return 0;
> }
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