transform_auto_correlate_fft() [1/2]

template<OperationReadyData DataType>

DataType MayaFlux::Yantra::transform_auto_correlate_fft	(	DataType &	input,
		bool	normalize = true
	)

Auto-correlation using FFT (IN-PLACE)

Template Parameters

DataType

OperationReadyData type

Parameters

input	Input data - will be modified
normalize	Whether to normalize the result

Returns

Auto-correlated data

Definition at line 326 of file ConvolutionHelper.hpp.

{
    auto [target_data, structure_info] = OperationHelper::extract_structured_double(input);
 
    // For auto-correlation using FFT:
    // R(k) = IFFT(FFT(x) * conj(FFT(x)))
 
    auto correlation_op = [](const Eigen::VectorXcd& input_fft,
                              const Eigen::VectorXcd& /* unused */,
                              Eigen::VectorXcd& result_fft) {
        std::ranges::transform(input_fft, input_fft, result_fft.begin(),
            [](const std::complex<double>& a, const std::complex<double>& b) {
                return a * std::conj(b);
            });
    };
 
    for (auto& span : target_data) {
        std::vector<double> signal_copy(span.begin(), span.end());
        auto result = fft_convolve_helper(span, signal_copy, correlation_op);
 
        if (normalize && !result.empty()) {
            double max_val = *std::max_element(result.begin(), result.end());
            if (max_val > 0.0) {
                std::ranges::transform(result, result.begin(),
                    [max_val](double val) { return val / max_val; });
            }
        }
 
        std::copy(result.begin(), result.begin() + std::min(result.size(), span.size()), span.begin());
    }
 
    auto reconstructed_data = target_data
        | std::views::transform([](const auto& span) {
              return std::vector<double>(span.begin(), span.end());
          })
        | std::ranges::to<std::vector>();
 
    return OperationHelper::reconstruct_from_double<DataType>(reconstructed_data, structure_info);
}

References MayaFlux::Yantra::OperationHelper::extract_structured_double(), fft_convolve_helper(), and MayaFlux::normalize().

Referenced by MayaFlux::Yantra::ConvolutionTransformer< InputType, OutputType >::transform_implementation().

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