root-6.10.00/html/simple_8cxx.html

/*************************************************************************

 * Copyright (C) 1995-2015, Rene Brun and Fons Rademakers.               *

 * All rights reserved.                                                  *

 *                                                                       *

 * For the licensing terms see $ROOTSYS/LICENSE.                         *

 * For the list of contributors see $ROOTSYS/README/CREDITS.             *

 *************************************************************************/


#include "ROOT/THist.hxx"

#include "ROOT/TFit.hxx"

#include "ROOT/TFile.hxx"


void simple() {

  using namespace ROOT;


  // Create a 2D histogram with an X axis with equidistant bins, and a y axis

  // with irregular binning.

  Experimental::TAxisConfig xAxis(100, 0., 1.);

  Experimental::TAxisConfig yAxis({0., 1., 2., 3.,10.});

  Experimental::TH2D histFromVars(xAxis, yAxis);


  // Or the short in-place version:

  // Create a 2D histogram with an X axis with equidistant bins, and a y axis

  // with irregular binning.

  Experimental::TH2D hist({100, 0., 1.}, {{0., 1., 2., 3.,10.}});


  // Fill weight 1. at the coordinate 0.01, 1.02.

  hist.Fill({0.01, 1.02});


  // Fit the histogram.

  Experimental::TFunction<2> func([](const std::array<double,2>& x,

                             const std::array_view<double>& par)

                          { return par[0]*x[0]*x[0] + (par[1]-x[1])*x[1]; });


  Experimental::TFitResult fitResult = Experimental::FitTo(hist, func, {{0., 1.}});


  Experimental::TFilePtr file = Experimental::TFile::Recreate("hist.root");

  file->Write("TheHist", hist);

}