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58 lines
2.2 KiB
C++
58 lines
2.2 KiB
C++
// Copyright 2019 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_axis_with_transform
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#include <boost/histogram/axis/regular.hpp>
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#include <limits>
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int main() {
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using namespace boost::histogram;
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// make a regular axis with a log transform over [10, 100), [100, 1000), [1000, 10000)
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axis::regular<double, axis::transform::log> r_log{3, 10., 10000.};
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// log transform:
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// - useful when values vary dramatically in magnitude, like brightness of stars
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// - edges are not exactly at 10, 100, 1000, because of finite floating point precision
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// - value >= 0 below is mapped to -1
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// - value < 0 below is mapped to `size()`, because the result of std::log is NaN
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assert(r_log.index(10.1) == 0);
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assert(r_log.index(100.1) == 1);
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assert(r_log.index(1000.1) == 2);
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assert(r_log.index(1) == -1);
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assert(r_log.index(0) == -1);
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assert(r_log.index(-1) == 3);
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// make a regular axis with a sqrt transform over [4, 9), [9, 16), [16, 25)
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axis::regular<double, axis::transform::sqrt> r_sqrt{3, 4., 25.};
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// sqrt transform:
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// - bin widths are more mildly increasing compared to log transform
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// - starting axis at value == 0 is ok, sqrt(0) == 0 unlike log transform
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// - value < 0 is mapped to `size()`, because the result of std::sqrt is NaN
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assert(r_sqrt.index(0) == -1);
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assert(r_sqrt.index(4.1) == 0);
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assert(r_sqrt.index(9.1) == 1);
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assert(r_sqrt.index(16.1) == 2);
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assert(r_sqrt.index(25.1) == 3);
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assert(r_sqrt.index(-1) == 3);
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// make a regular axis with a power transform x^1/3 over [1, 8), [8, 27), [27, 64)
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using pow_trans = axis::transform::pow;
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axis::regular<double, pow_trans> r_pow(pow_trans{1. / 3.}, 3, 1., 64.);
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// pow transform:
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// - generalization of the sqrt transform, power index is first argument of ctor
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// - starting the axis at value == 0 is ok, 0^p == 0 for p != 0
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// - value < 0 is mapped to `size()`, because the result of std::pow is NaN
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assert(r_pow.index(0) == -1);
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assert(r_pow.index(1.1) == 0);
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assert(r_pow.index(8.1) == 1);
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assert(r_pow.index(27.1) == 2);
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assert(r_pow.index(64.1) == 3);
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assert(r_pow.index(-1) == 3);
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}
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//]
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