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- // Copyright 2015-2018 Hans Dembinski
- //
- // Distributed under the Boost Software License, Version 1.0.
- // (See accompanying file LICENSE_1_0.txt
- // or copy at http://www.boost.org/LICENSE_1_0.txt)
- //[ guide_histogram_operators
- #include <boost/histogram.hpp>
- #include <cassert>
- #include <vector>
- int main() {
- using namespace boost::histogram;
- // make two histograms
- auto h1 = make_histogram(axis::regular<>(2, -1.0, 1.0));
- auto h2 = make_histogram(axis::regular<>(2, -1.0, 1.0));
- 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 likely to be optimized by the compiler so that
- // superfluous temporaries avoided, but no guarantees are given; use this equivalent
- // code when you want to make sure: h4 = h1; h4 += h2; h4 += h3;
- auto h4 = h1 + h2 + h3; // counts are: 2 2
- assert(h4.at(0) == 2 && h4.at(1) == 2);
- // multiply by number, h4 *= 2 also works
- auto h5 = h4 * 2; // counts are: 4 4
- // divide by number; s4 /= 4 also works
- auto h6 = h5 / 4; // counts are: 1 1
- assert(h6.at(0) == 1 && h6.at(1) == 1);
- assert(h6 != h5 && h5 == 4 * h6);
- // note the special effect of multiplication on weight_storage
- auto h = make_histogram_with(weight_storage(), axis::regular<>(2, -1.0, 1.0));
- h(-0.5);
- // counts are: 1 0
- assert(h.at(0).value() == 1 && h.at(1).value() == 0);
- auto h_sum = h + h;
- auto h_mul = 2 * h;
- // values are the same as expected...
- assert(h_sum.at(0).value() == h_mul.at(0).value());
- // ... but variances differ
- assert(h_sum.at(0).variance() == 2 && h_mul.at(0).variance() == 4);
- // equality operator checks variances, so histograms are not equal
- assert(h_sum != h_mul);
- }
- //]
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