kopia lustrzana https://github.com/vsamy/DiFipp
43 wiersze
1.3 KiB
C++
43 wiersze
1.3 KiB
C++
#pragma once
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#include "type_checks.h"
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#include "typedefs.h"
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#include <complex>
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namespace fratio {
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template <typename T>
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struct VietaAlgo {
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static_assert(std::is_arithmetic<internal::complex_sub_type_t<T>>::value, "This struct can only accept arithmetic types or complex.");
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// Vieta's computation: https://en.wikipedia.org/wiki/Vieta%27s_formulas
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static Eigen::VectorX<T> polyCoeffFromRoot(const Eigen::VectorX<T>& poles);
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};
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template <typename T>
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Eigen::VectorX<T> VietaAlgo<T>::polyCoeffFromRoot(const Eigen::VectorX<T>& poles)
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{
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Eigen::VectorX<T> coeffs = Eigen::VectorX<T>::Zero(poles.size() + 1);
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coeffs(0) = T(1);
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for (Eigen::Index i = 0; i < poles.size(); ++i) {
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for (Eigen::Index k = i + 1; k > 0; --k) {
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coeffs(k) -= poles(i) * coeffs(k - 1);
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}
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}
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// Check for equation c(k) = sum(i=k-1, poles.size() : p(i)) * c(k-1), k>=1
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// Eigen::Index pSize = poles.size();
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// for (Eigen::Index k = 1; k < coeffs.size(); ++k)
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// coeffs(k) -= poles.tail(pSize - (k - 1)).sum() * coeffs(k - 1);
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// Maybe better
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// T sum = poles.sum();
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// for (Eigen::Index k = 1; k < coeffs.size(); ++k) {
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// coeffs(k) -= sum * coeffs(k - 1);
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// sum -= poles(k - 1);
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// }
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return coeffs;
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}
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} // namespace fratio
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