Function main

examples/guide_histogram_operators.cpp:8–55

namespace bh = boost::histogram;

int main() {
  // make two histograms
  auto h1 = bh::make_static_histogram(bh::axis::regular<>(2, -1, 1));
  auto h2 = bh::make_static_histogram(bh::axis::regular<>(2, -1, 1));

  h1(-0.5); // counts are: 1 0
  h2(0.5);  // counts are: 0 1

  // add them
  auto h3 = h1;
  h3 += h2; // counts are: 1 1

  // adding multiple histograms at once is efficient and does not create
  // superfluous temporaries since operator+ functions are overloaded to
  // accept and return rvalue references where possible
  auto h4 = h1 + h2 + h3; // counts are: 2 2

  std::cout << h4.at(0).value() << " " << h4.at(1).value() << std::endl;
  // prints: 2 2

  // multiply by number
  h4 *= 2; // counts are: 4 4

  // divide by number
  auto h5 = h4 / 4; // counts are: 1 1

  std::cout << h5.at(0).value() << " " << h5.at(1).value() << std::endl;
  // prints: 1 1

  // compare histograms
  std::cout << (h4 == 4 * h5) << " " << (h4 != h5) << std::endl;
  // prints: 1 1

  // note: special effect of multiplication on counter variance
  auto h = bh::make_static_histogram(bh::axis::regular<>(2, -1, 1));
  h(-0.5); // counts are: 1 0
  std::cout << "value    " << (2 * h).at(0).value() << " "
            << (h + h).at(0).value() << "\n"
            << "variance " << (2 * h).at(0).variance() << " "
            << (h + h).at(0).variance() << std::endl;
  // equality operator also checks variances, so the statement is false
  std::cout << (h + h == 2 * h) << std::endl;
  /* prints:
      value    2 2
      variance 4 2
      0
  */
}

//]