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95 lines
2.6 KiB
C++
95 lines
2.6 KiB
C++
//===----------------------------------------------------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is dual licensed under the MIT and the University of Illinois Open
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// Source Licenses. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// REQUIRES: long_tests
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// <random>
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// template<class RealType = double>
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// class piecewise_linear_distribution
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// template<class _URNG> result_type operator()(_URNG& g, const param_type& parm);
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#include <random>
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#include <vector>
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#include <iterator>
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#include <numeric>
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#include <algorithm> // for sort
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#include <cassert>
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#include <limits>
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template <class T>
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inline
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T
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sqr(T x)
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{
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return x*x;
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}
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double
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f(double x, double a, double m, double b, double c)
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{
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return a + m*(sqr(x) - sqr(b))/2 + c*(x-b);
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}
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int main()
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{
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{
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typedef std::piecewise_linear_distribution<> D;
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typedef D::param_type P;
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typedef std::mt19937_64 G;
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G g;
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double b[] = {10, 14, 16, 17};
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double p[] = {25, 62.5, 12.5, 0};
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const size_t Np = sizeof(p) / sizeof(p[0]) - 1;
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D d;
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P pa(b, b+Np+1, p);
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const size_t N = 1000000;
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std::vector<D::result_type> u;
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for (size_t i = 0; i < N; ++i)
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{
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D::result_type v = d(g, pa);
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assert(10 <= v && v < 17);
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u.push_back(v);
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}
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std::sort(u.begin(), u.end());
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int kp = -1;
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double a = std::numeric_limits<double>::quiet_NaN();
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double m = std::numeric_limits<double>::quiet_NaN();
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double bk = std::numeric_limits<double>::quiet_NaN();
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double c = std::numeric_limits<double>::quiet_NaN();
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std::vector<double> areas(Np);
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double S = 0;
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for (size_t i = 0; i < areas.size(); ++i)
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{
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areas[i] = (p[i]+p[i+1])*(b[i+1]-b[i])/2;
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S += areas[i];
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}
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for (size_t i = 0; i < areas.size(); ++i)
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areas[i] /= S;
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for (size_t i = 0; i < Np+1; ++i)
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p[i] /= S;
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for (size_t i = 0; i < N; ++i)
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{
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int k = std::lower_bound(b, b+Np+1, u[i]) - b - 1;
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if (k != kp)
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{
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a = 0;
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for (int j = 0; j < k; ++j)
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a += areas[j];
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m = (p[k+1] - p[k]) / (b[k+1] - b[k]);
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bk = b[k];
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c = (b[k+1]*p[k] - b[k]*p[k+1]) / (b[k+1] - b[k]);
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kp = k;
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}
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assert(std::abs(f(u[i], a, m, bk, c) - double(i)/N) < .001);
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}
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}
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}
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