ceph/src/boost/libs/histogram/examples/guide_histogram_operators.cpp

   1 // Copyright 2015-2018 Hans Dembinski
   2 //
   3 // Distributed under the Boost Software License, Version 1.0.
   4 // (See accompanying file LICENSE_1_0.txt
   5 // or copy at http://www.boost.org/LICENSE_1_0.txt)
   6
   7 //[ guide_histogram_operators
   8
   9 #include <boost/histogram.hpp>
  10 #include <cassert>
  11 #include <vector>
  12
  13 int main() {
  14   using namespace boost::histogram;
  15
  16   // make two histograms
  17   auto h1 = make_histogram(axis::regular<>(2, -1.0, 1.0));
  18   auto h2 = make_histogram(axis::regular<>(2, -1.0, 1.0));
  19
  20   h1(-0.5); // counts are: 1 0
  21   h2(0.5);  // counts are: 0 1
  22
  23   // add them
  24   auto h3 = h1;
  25   h3 += h2; // counts are: 1 1
  26
  27   // adding multiple histograms at once is likely to be optimized by the compiler so that
  28   // superfluous temporaries avoided, but no guarantees are given; use this equivalent
  29   // code when you want to make sure: h4 = h1; h4 += h2; h4 += h3;
  30   auto h4 = h1 + h2 + h3; // counts are: 2 2
  31
  32   assert(h4.at(0) == 2 && h4.at(1) == 2);
  33
  34   // multiply by number, h4 *= 2 also works
  35   auto h5 = h4 * 2; // counts are: 4 4
  36
  37   // divide by number; s4 /= 4 also works
  38   auto h6 = h5 / 4; // counts are: 1 1
  39
  40   assert(h6.at(0) == 1 && h6.at(1) == 1);
  41   assert(h6 != h5 && h5 == 4 * h6);
  42
  43   // note the special effect of multiplication on weight_storage
  44   auto h = make_histogram_with(weight_storage(), axis::regular<>(2, -1.0, 1.0));
  45   h(-0.5);
  46
  47   // counts are: 1 0
  48   assert(h.at(0).value() == 1 && h.at(1).value() == 0);
  49
  50   auto h_sum = h + h;
  51   auto h_mul = 2 * h;
  52
  53   // values are the same as expected...
  54   assert(h_sum.at(0).value() == h_mul.at(0).value());
  55   // ... but variances differ
  56   assert(h_sum.at(0).variance() == 2 && h_mul.at(0).variance() == 4);
  57
  58   // equality operator checks variances, so histograms are not equal
  59   assert(h_sum != h_mul);
  60 }
  61
  62 //]