spectral_spread.hpp

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#ifndef EDSP_SPECTRAL_SPREAD_HPP
#define EDSP_SPECTRAL_SPREAD_HPP

#include <edsp/feature/spectral/spectral_centroid.hpp>
#include <cmath>

namespace edsp { namespace feature { inline namespace spectral {

    template <typename ForwardIt>
    constexpr auto spectral_spread(ForwardIt first1, ForwardIt last1, ForwardIt first2) {
        using value_type = typename std::iterator_traits<ForwardIt>::value_type ;
        const auto centroid = feature::spectral_centroid(first1, last1, first2);
        auto weighted_sum   = static_cast<value_type>(0);
        auto unweighted_sum = static_cast<value_type>(0);
        for (value_type i = 0; first1 != last1; ++first1, ++i) {
            const auto diff = i - centroid;
            weighted_sum += (diff * diff) * (*first1);
            unweighted_sum += *first1;
        }
        return static_cast<value_type>(std::sqrt(weighted_sum / unweighted_sum));
    }

}}}


#endif //EDSP_SPECTRAL_SPREAD_HPP