TTree* read (const TString& filename, Int_t ncol) 
  {
    TString vars;

    Int_t nlin=0;

    for (Int_t i = 0; i < ncol; i++) {
      vars += Form("x%d", i); 
      if (i==0) vars += "/D"; 
      if (i + 1 != ncol) vars += ":";
    }

    TArrayD x(ncol);
    TTree* tree = new TTree("tree", "Tree"); 
    tree->Branch("data", &x.fArray, vars.Data());
    
    ifstream in(filename.Data());
    if (!in || in.bad()) return 1;
    
    while (!in.eof()) {
      x.Reset();
      for (Int_t i = 0; i < ncol; i++) in >> x[i];
      nlin++;
      tree->Fill();
    }

    in.close();
  
    cout<<nlin<<" lines"<<endl;
    tree->Print();
    return tree;
  }