doc/v614/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::span<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);
}