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64 lines
1.9 KiB
C++
64 lines
1.9 KiB
C++
// Copyright 2015-2018 Hans Dembinski
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//
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// Distributed under the Boost Software License, Version 1.0.
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// (See accompanying file LICENSE_1_0.txt
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// or copy at http://www.boost.org/LICENSE_1_0.txt)
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//[ guide_histogram_operators
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#include <boost/histogram.hpp>
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#include <cassert>
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#include <vector>
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int main() {
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using namespace boost::histogram;
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// make two histograms
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auto h1 = make_histogram(axis::regular<>(2, -1.0, 1.0));
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auto h2 = make_histogram(axis::regular<>(2, -1.0, 1.0));
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h1(-0.5); // counts are: 1 0
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h2(0.5); // counts are: 0 1
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// add them
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auto h3 = h1;
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h3 += h2; // counts are: 1 1
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// adding multiple histograms at once is likely to be optimized by the compiler so that
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// superfluous temporaries avoided, but no guarantees are given; use this equivalent
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// code when you want to make sure: h4 = h1; h4 += h2; h4 += h3;
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auto h4 = h1 + h2 + h3; // counts are: 2 2
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assert(h4.at(0) == 2 && h4.at(1) == 2);
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// multiply by number; h4 *= 2 is not allowed, because the result of a multiplication is
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// not a histogram anymore, it has the type boost::histogram::grid<...>)
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auto g4 = h4 * 2; // counts are: 4 4
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// divide by number; g4 /= 4 also works
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auto g5 = g4 / 4; // counts are: 1 1
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assert(g5.at(0) == 1 && g5.at(1) == 1);
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assert(g4 != g5 && g4 == 4 * g5);
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// note special effect of multiplication on weighted_sum
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auto h = make_histogram_with(std::vector<accumulators::weighted_sum<double>>(),
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axis::regular<>(2, -1.0, 1.0));
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h(-0.5);
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// counts are: 1 0
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assert(h.at(0).value() == 1 && h.at(1).value() == 0);
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auto h_sum = h + h; // value 2 0 variance 2 0
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auto g_mul = 2 * h; // value 2 0 variance 4 0
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// equality operator checks variances, so following statement is false
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assert(h_sum != g_mul);
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// variance is different when histograms are scaled
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assert(h_sum.at(0).value() == g_mul.at(0).value());
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assert(h_sum.at(0).variance() == 2 && g_mul.at(0).variance() == 4);
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}
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//]
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