spectral_variation.hpp

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#ifndef EDSP_SPECTRAL_VARIATION_HPP
#define EDSP_SPECTRAL_VARIATION_HPP

#include <iterator>
#include <cmath>

namespace edsp { namespace feature { inline namespace spectral {

    template <typename ForwardIt>
    constexpr auto spectral_variation(ForwardIt first1, ForwardIt last1, ForwardIt first2) {
        using value_type = typename std::iterator_traits<ForwardIt>::value_type ;
        auto sum_x1 = static_cast<value_type >(0);
        auto sum_x2 = static_cast<value_type >(0);
        auto sum_x12 = static_cast<value_type >(0);
        for (; first1 != last1; ++first1, ++first2) {
            sum_x1 += *first1;
            sum_x2 += *first2;
            sum_x12 += *first1 * *first2;
        }
        return 1 - sum_x2 / (std::sqrt(sum_x1) * std::sqrt(sum_x2));
    }

}}}

#endif //EDSP_SPECTRAL_VARIATION_HPP