spectral_slope.hpp

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#ifndef EDSP_SPECTRAL_SLOPE_HPP
#define EDSP_SPECTRAL_SLOPE_HPP

#include <iterator>

namespace edsp { namespace feature { inline namespace spectral {


    template <typename ForwardIt>
    constexpr auto spectral_slope(ForwardIt first1, ForwardIt last1, ForwardIt first2) {
        using value_type = typename std::iterator_traits<ForwardIt>::value_type ;
        auto m_sum  = static_cast<value_type>(0);
        auto f_sum  = static_cast<value_type>(0);
        auto ff_sum = static_cast<value_type>(0);
        auto mf_sum = static_cast<value_type >(0);
        for (; first1 != last1; ++first1, ++first2) {
            m_sum += *first1;
            f_sum += *first2;
            mf_sum += (*first1) * (*first2);
            ff_sum += (*first2) * (*first2);
        }
        const auto N = static_cast<value_type >(std::distance(first1, last1));
        return (1 / m_sum) * (N * mf_sum - f_sum * m_sum) / (N * ff_sum - (f_sum * f_sum));
    }

}}}

#endif //EDSP_SPECTRAL_SLOPE_HPP