1 // (C) Copyright Nick Thompson 2018.
2 // Use, modification and distribution are subject to the
3 // Boost Software License, Version 1.0. (See accompanying file
4 // LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6 #ifndef BOOST_MATH_TOOLS_SIGNAL_STATISTICS_HPP
7 #define BOOST_MATH_TOOLS_SIGNAL_STATISTICS_HPP
11 #include <boost/assert.hpp>
12 #include <boost/math/tools/complex.hpp>
13 #include <boost/math/tools/roots.hpp>
14 #include <boost/math/statistics/univariate_statistics.hpp>
15 #include <boost/config/header_deprecated.hpp>
17 BOOST_HEADER_DEPRECATED("<boost/math/statistics/signal_statistics.hpp>");
19 namespace boost::math::tools {
21 template<class ForwardIterator>
22 auto absolute_gini_coefficient(ForwardIterator first, ForwardIterator last)
25 using RealOrComplex = typename std::iterator_traits<ForwardIterator>::value_type;
26 BOOST_ASSERT_MSG(first != last && std::next(first) != last, "Computation of the Gini coefficient requires at least two samples.");
28 std::sort(first, last, [](RealOrComplex a, RealOrComplex b) { return abs(b) > abs(a); });
31 decltype(abs(*first)) i = 1;
32 decltype(abs(*first)) num = 0;
33 decltype(abs(*first)) denom = 0;
34 for (auto it = first; it != last; ++it)
36 decltype(abs(*first)) tmp = abs(*it);
42 // If the l1 norm is zero, all elements are zero, so every element is the same.
45 decltype(abs(*first)) zero = 0;
48 return ((2*num)/denom - i)/(i-1);
51 template<class RandomAccessContainer>
52 inline auto absolute_gini_coefficient(RandomAccessContainer & v)
54 return boost::math::tools::absolute_gini_coefficient(v.begin(), v.end());
57 template<class ForwardIterator>
58 auto sample_absolute_gini_coefficient(ForwardIterator first, ForwardIterator last)
60 size_t n = std::distance(first, last);
61 return n*boost::math::tools::absolute_gini_coefficient(first, last)/(n-1);
64 template<class RandomAccessContainer>
65 inline auto sample_absolute_gini_coefficient(RandomAccessContainer & v)
67 return boost::math::tools::sample_absolute_gini_coefficient(v.begin(), v.end());
71 // The Hoyer sparsity measure is defined in:
72 // https://arxiv.org/pdf/0811.4706.pdf
73 template<class ForwardIterator>
74 auto hoyer_sparsity(const ForwardIterator first, const ForwardIterator last)
76 using T = typename std::iterator_traits<ForwardIterator>::value_type;
79 BOOST_ASSERT_MSG(first != last && std::next(first) != last, "Computation of the Hoyer sparsity requires at least two samples.");
81 if constexpr (std::is_unsigned<T>::value)
86 for (auto it = first; it != last; ++it)
93 double rootn = sqrt(n);
94 return (rootn - l1/sqrt(l2) )/ (rootn - 1);
97 decltype(abs(*first)) l1 = 0;
98 decltype(abs(*first)) l2 = 0;
99 // We wouldn't need to count the elements if it was a random access iterator,
100 // but our only constraint is that it's a forward iterator.
102 for (auto it = first; it != last; ++it)
104 decltype(abs(*first)) tmp = abs(*it);
109 if constexpr (std::is_integral<T>::value)
111 double rootn = sqrt(n);
112 return (rootn - l1/sqrt(l2) )/ (rootn - 1);
116 decltype(abs(*first)) rootn = sqrt(static_cast<decltype(abs(*first))>(n));
117 return (rootn - l1/sqrt(l2) )/ (rootn - 1);
122 template<class Container>
123 inline auto hoyer_sparsity(Container const & v)
125 return boost::math::tools::hoyer_sparsity(v.cbegin(), v.cend());
129 template<class Container>
130 auto oracle_snr(Container const & signal, Container const & noisy_signal)
132 using Real = typename Container::value_type;
133 BOOST_ASSERT_MSG(signal.size() == noisy_signal.size(),
134 "Signal and noisy_signal must be have the same number of elements.");
135 if constexpr (std::is_integral<Real>::value)
137 double numerator = 0;
138 double denominator = 0;
139 for (size_t i = 0; i < signal.size(); ++i)
141 numerator += signal[i]*signal[i];
142 denominator += (noisy_signal[i] - signal[i])*(noisy_signal[i] - signal[i]);
144 if (numerator == 0 && denominator == 0)
146 return std::numeric_limits<double>::quiet_NaN();
148 if (denominator == 0)
150 return std::numeric_limits<double>::infinity();
152 return numerator/denominator;
154 else if constexpr (boost::math::tools::is_complex_type<Real>::value)
158 typename Real::value_type numerator = 0;
159 typename Real::value_type denominator = 0;
160 for (size_t i = 0; i < signal.size(); ++i)
162 numerator += norm(signal[i]);
163 denominator += norm(noisy_signal[i] - signal[i]);
165 if (numerator == 0 && denominator == 0)
167 return std::numeric_limits<typename Real::value_type>::quiet_NaN();
169 if (denominator == 0)
171 return std::numeric_limits<typename Real::value_type>::infinity();
174 return numerator/denominator;
179 Real denominator = 0;
180 for (size_t i = 0; i < signal.size(); ++i)
182 numerator += signal[i]*signal[i];
183 denominator += (signal[i] - noisy_signal[i])*(signal[i] - noisy_signal[i]);
185 if (numerator == 0 && denominator == 0)
187 return std::numeric_limits<Real>::quiet_NaN();
189 if (denominator == 0)
191 return std::numeric_limits<Real>::infinity();
194 return numerator/denominator;
198 template<class Container>
199 auto mean_invariant_oracle_snr(Container const & signal, Container const & noisy_signal)
201 using Real = typename Container::value_type;
202 BOOST_ASSERT_MSG(signal.size() == noisy_signal.size(), "Signal and noisy signal must be have the same number of elements.");
204 Real mu = boost::math::tools::mean(signal);
206 Real denominator = 0;
207 for (size_t i = 0; i < signal.size(); ++i)
209 Real tmp = signal[i] - mu;
210 numerator += tmp*tmp;
211 denominator += (signal[i] - noisy_signal[i])*(signal[i] - noisy_signal[i]);
213 if (numerator == 0 && denominator == 0)
215 return std::numeric_limits<Real>::quiet_NaN();
217 if (denominator == 0)
219 return std::numeric_limits<Real>::infinity();
222 return numerator/denominator;
226 template<class Container>
227 auto mean_invariant_oracle_snr_db(Container const & signal, Container const & noisy_signal)
230 return 10*log10(boost::math::tools::mean_invariant_oracle_snr(signal, noisy_signal));
234 // Follows the definition of SNR given in Mallat, A Wavelet Tour of Signal Processing, equation 11.16.
235 template<class Container>
236 auto oracle_snr_db(Container const & signal, Container const & noisy_signal)
239 return 10*log10(boost::math::tools::oracle_snr(signal, noisy_signal));
242 // A good reference on the M2M4 estimator:
243 // D. R. Pauluzzi and N. C. Beaulieu, "A comparison of SNR estimation techniques for the AWGN channel," IEEE Trans. Communications, Vol. 48, No. 10, pp. 1681-1691, 2000.
244 // A nice python implementation:
245 // https://github.com/gnuradio/gnuradio/blob/master/gr-digital/examples/snr_estimators.py
246 template<class ForwardIterator>
247 auto m2m4_snr_estimator(ForwardIterator first, ForwardIterator last, decltype(*first) estimated_signal_kurtosis=1, decltype(*first) estimated_noise_kurtosis=3)
249 BOOST_ASSERT_MSG(estimated_signal_kurtosis > 0, "The estimated signal kurtosis must be positive");
250 BOOST_ASSERT_MSG(estimated_noise_kurtosis > 0, "The estimated noise kurtosis must be positive.");
251 using Real = typename std::iterator_traits<ForwardIterator>::value_type;
253 if constexpr (std::is_floating_point<Real>::value || std::numeric_limits<Real>::max_exponent)
255 // If we first eliminate N, we obtain the quadratic equation:
256 // (ka+kw-6)S^2 + 2M2(3-kw)S + kw*M2^2 - M4 = 0 =: a*S^2 + bs*N + cs = 0
257 // If we first eliminate S, we obtain the quadratic equation:
258 // (ka+kw-6)N^2 + 2M2(3-ka)N + ka*M2^2 - M4 = 0 =: a*N^2 + bn*N + cn = 0
259 // I believe these equations are totally independent quadratics;
260 // if one has a complex solution it is not necessarily the case that the other must also.
261 // However, I can't prove that, so there is a chance that this does unnecessary work.
262 // Future improvements: There are algorithms which can solve quadratics much more effectively than the naive implementation found here.
263 // See: https://stackoverflow.com/questions/48979861/numerically-stable-method-for-solving-quadratic-equations/50065711#50065711
264 auto [M1, M2, M3, M4] = boost::math::tools::first_four_moments(first, last);
267 // The signal is constant. There is no noise:
268 return std::numeric_limits<Real>::infinity();
270 // Change to notation in Pauluzzi, equation 41:
271 auto kw = estimated_noise_kurtosis;
272 auto ka = estimated_signal_kurtosis;
273 // A common case, since it's the default:
275 Real bs = 2*M2*(3-kw);
276 Real cs = kw*M2*M2 - M4;
277 Real bn = 2*M2*(3-ka);
278 Real cn = ka*M2*M2 - M4;
279 auto [S0, S1] = boost::math::tools::quadratic_roots(a, bs, cs);
296 auto [N0, N1] = boost::math::tools::quadratic_roots(a, bn, cn);
313 // This happens distressingly often. It's a limitation of the method.
314 return std::numeric_limits<Real>::quiet_NaN();
318 BOOST_ASSERT_MSG(false, "The M2M4 estimator has not been implemented for this type.");
319 return std::numeric_limits<Real>::quiet_NaN();
323 template<class Container>
324 inline auto m2m4_snr_estimator(Container const & noisy_signal, typename Container::value_type estimated_signal_kurtosis=1, typename Container::value_type estimated_noise_kurtosis=3)
326 return m2m4_snr_estimator(noisy_signal.cbegin(), noisy_signal.cend(), estimated_signal_kurtosis, estimated_noise_kurtosis);
329 template<class ForwardIterator>
330 inline auto m2m4_snr_estimator_db(ForwardIterator first, ForwardIterator last, decltype(*first) estimated_signal_kurtosis=1, decltype(*first) estimated_noise_kurtosis=3)
333 return 10*log10(m2m4_snr_estimator(first, last, estimated_signal_kurtosis, estimated_noise_kurtosis));
337 template<class Container>
338 inline auto m2m4_snr_estimator_db(Container const & noisy_signal, typename Container::value_type estimated_signal_kurtosis=1, typename Container::value_type estimated_noise_kurtosis=3)
341 return 10*log10(m2m4_snr_estimator(noisy_signal, estimated_signal_kurtosis, estimated_noise_kurtosis));