C++ TRandom::Landau方法代码示例

void tv3Write() {
   //creates the Tree
   TVector3 *v = new TVector3();
   TVector3::Class()->IgnoreTObjectStreamer();
   TFile *f = new TFile("v3.root","recreate");
   TTree *T = new TTree("T","v3 Tree");
   T->Branch("v3","TVector3",&v,32000,1);
   TRandom r;
   for (Int_t i=0;i<10000;i++) {
      v->SetXYZ(r.Gaus(0,1),r.Landau(0,1),r.Gaus(100,10));
      T->Fill();
   }
   T->Write();
   T->Print();
   delete f;
}

void CreateParentTree() {
   // create a simple TTree with 5 branches
   // Two branches ("Run" and "Event") will be used to index the Tree
   TFile *f = new TFile("treeparent.root","recreate");
   TTree *T = new TTree("T","test friend trees");
   T->Branch("Run",&Run,"Run/I");
   T->Branch("Event",&Event,"Event/I");
   T->Branch("x",&x,"x/F");
   T->Branch("y",&y,"y/F");
   T->Branch("z",&z,"z/F");
   TRandom r;
   for (Int_t i=0;i<10000;i++) {
      if (i < 5000) Run = 1;
      else          Run = 2;
      Event = i;
      x = r.Gaus(10,1);
      y = r.Gaus(20,2);
      z = r.Landau(2,1);
      T->Fill();
   }
   T->Print();
   T->Write();
   delete f;
}

//_____________________________________________________________________________
Int_t ProofAux::GenerateTree(const char *fnt, Long64_t ent, TString &fn)
{
   // Generate the main tree for the 'friends' tutorial; the tree is called
   // 'Tmain', has 'ent' entries and is saved to file 'fnt'.
   // The full file path is returned in 'fn'.
   // Return 0 on success, -1 on error.

   Int_t rc = -1;

   // Check the filename
   fn = fnt;
   if (fn.IsNull()) {
      Error("GenerateTree", "file name undefined!");
      return rc;
   }
   TUrl uu(fn, kTRUE);
   if (!strcmp(uu.GetProtocol(), "file") && !fn.BeginsWith("/")) {
      // Local file with relative path: create under the data directory
      if (!gProofServ ||
          !(gProofServ->GetDataDir()) || strlen(gProofServ->GetDataDir()) <= 0) {
         Error("GenerateTree", "data directory undefined!");
         return rc;
      }
      // Insert data directory
      fn.Insert(0, TString::Format("%s/", gProofServ->GetDataDir()));
      // Make sure the directory exists
      TString dir = gSystem->DirName(fn);
      if (gSystem->AccessPathName(dir, kWritePermission)) {
         if (gSystem->mkdir(dir, kTRUE) != 0) {
            Error("GenerateTree", "problems creating directory %s to store the file", dir.Data());
            return rc;
         }
      }
   }

   // Create the file
   TDirectory* savedir = gDirectory;
   TFile *f = new TFile(fn, "RECREATE");
   if (!f || f->IsZombie()) {
      Error("GenerateTree", "problems opening file %s", fn.Data());
      return rc;
   }
   savedir->cd();
   rc = 0;

   // Create the tree
   TTree *T = new TTree("Tmain","Main tree for tutorial friends");
   T->SetDirectory(f);
   Int_t Run = 1;
   T->Branch("Run",&Run,"Run/I");
   Long64_t Event = 0;
   T->Branch("Event",&Event,"Event/L");
   Float_t x = 0., y = 0., z = 0.;
   T->Branch("x",&x,"x/F");
   T->Branch("y",&y,"y/F");
   T->Branch("z",&z,"z/F");
   TRandom r;
   for (Long64_t i = 0; i < ent; i++) {
      if (i > 0 && i%1000 == 0) Run++;
      Event = i;
      x = r.Gaus(10,1);
      y = r.Gaus(20,2);
      z = r.Landau(2,1);
      T->Fill();
   }
   T->Print();
   f->cd();
   T->Write();
   T->SetDirectory(0);
   f->Close();
   delete f;
   delete T;

   // Notify success
   Info("GenerateTree", "file '%s' successfully created", fn.Data());

   // Add to the list
   TString fds(fn);
   if (!strcmp(uu.GetProtocol(), "file")) {
      if (gSystem->Getenv("LOCALDATASERVER")) {
         if (strcmp(TUrl(gSystem->Getenv("LOCALDATASERVER"), kTRUE).GetProtocol(), "file"))
            fds.Insert(0, TString::Format("%s/", gSystem->Getenv("LOCALDATASERVER")));
      } else {
         fds.Insert(0, TString::Format("root://%s/", gSystem->HostName()));
      }
   }
   fMainList->Add(new TObjString(fds));

   // Done
   return rc;
}