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2023-06-02 10:49:02 +08:00
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thirdparty/include/Spectra/LinAlg/UpperHessenbergEigen.h vendored Normal file
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// The code was adapted from Eigen/src/Eigenvaleus/EigenSolver.h
//
// Copyright (C) 2008 Gael Guennebaud <gael.guennebaud@inria.fr>
// Copyright (C) 2010,2012 Jitse Niesen <jitse@maths.leeds.ac.uk>
// Copyright (C) 2016-2022 Yixuan Qiu <yixuan.qiu@cos.name>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at https://mozilla.org/MPL/2.0/.
#ifndef SPECTRA_UPPER_HESSENBERG_EIGEN_H
#define SPECTRA_UPPER_HESSENBERG_EIGEN_H
#include <Eigen/Core>
#include <stdexcept>
#include "UpperHessenbergSchur.h"
namespace Spectra {
template <typename Scalar = double>
class UpperHessenbergEigen
{
private:
using Index = Eigen::Index;
using Matrix = Eigen::Matrix<Scalar, Eigen::Dynamic, Eigen::Dynamic>;
using Vector = Eigen::Matrix<Scalar, Eigen::Dynamic, 1>;
using GenericMatrix = Eigen::Ref<Matrix>;
using ConstGenericMatrix = const Eigen::Ref<const Matrix>;
using Complex = std::complex<Scalar>;
using ComplexMatrix = Eigen::Matrix<Complex, Eigen::Dynamic, Eigen::Dynamic>;
using ComplexVector = Eigen::Matrix<Complex, Eigen::Dynamic, 1>;
Index m_n; // Size of the matrix
UpperHessenbergSchur<Scalar> m_schur; // Schur decomposition solver
Matrix m_matT; // Schur T matrix
Matrix m_eivec; // Storing eigenvectors
ComplexVector m_eivalues; // Eigenvalues
bool m_computed;
void doComputeEigenvectors()
{
using std::abs;
const Index size = m_eivec.cols();
const Scalar eps = Eigen::NumTraits<Scalar>::epsilon();
// inefficient! this is already computed in RealSchur
Scalar norm(0);
for (Index j = 0; j < size; ++j)
{
norm += m_matT.row(j).segment((std::max)(j - 1, Index(0)), size - (std::max)(j - 1, Index(0))).cwiseAbs().sum();
}
// Backsubstitute to find vectors of upper triangular form
if (norm == Scalar(0))
return;
for (Index n = size - 1; n >= 0; n--)
{
Scalar p = m_eivalues.coeff(n).real();
Scalar q = m_eivalues.coeff(n).imag();
// Scalar vector
if (q == Scalar(0))
{
Scalar lastr(0), lastw(0);
Index l = n;
m_matT.coeffRef(n, n) = Scalar(1);
for (Index i = n - 1; i >= 0; i--)
{
Scalar w = m_matT.coeff(i, i) - p;
Scalar r = m_matT.row(i).segment(l, n - l + 1).dot(m_matT.col(n).segment(l, n - l + 1));
if (m_eivalues.coeff(i).imag() < Scalar(0))
{
lastw = w;
lastr = r;
}
else
{
l = i;
if (m_eivalues.coeff(i).imag() == Scalar(0))
{
if (w != Scalar(0))
m_matT.coeffRef(i, n) = -r / w;
else
m_matT.coeffRef(i, n) = -r / (eps * norm);
}
else // Solve real equations
{
Scalar x = m_matT.coeff(i, i + 1);
Scalar y = m_matT.coeff(i + 1, i);
Scalar denom = (m_eivalues.coeff(i).real() - p) * (m_eivalues.coeff(i).real() - p) + m_eivalues.coeff(i).imag() * m_eivalues.coeff(i).imag();
Scalar t = (x * lastr - lastw * r) / denom;
m_matT.coeffRef(i, n) = t;
if (abs(x) > abs(lastw))
m_matT.coeffRef(i + 1, n) = (-r - w * t) / x;
else
m_matT.coeffRef(i + 1, n) = (-lastr - y * t) / lastw;
}
// Overflow control
Scalar t = abs(m_matT.coeff(i, n));
if ((eps * t) * t > Scalar(1))
m_matT.col(n).tail(size - i) /= t;
}
}
}
else if (q < Scalar(0) && n > 0)
{ // Complex vector
Scalar lastra(0), lastsa(0), lastw(0);
Index l = n - 1;
// Last vector component imaginary so matrix is triangular
if (abs(m_matT.coeff(n, n - 1)) > abs(m_matT.coeff(n - 1, n)))
{
m_matT.coeffRef(n - 1, n - 1) = q / m_matT.coeff(n, n - 1);
m_matT.coeffRef(n - 1, n) = -(m_matT.coeff(n, n) - p) / m_matT.coeff(n, n - 1);
}
else
{
Complex cc = Complex(Scalar(0), -m_matT.coeff(n - 1, n)) / Complex(m_matT.coeff(n - 1, n - 1) - p, q);
m_matT.coeffRef(n - 1, n - 1) = Eigen::numext::real(cc);
m_matT.coeffRef(n - 1, n) = Eigen::numext::imag(cc);
}
m_matT.coeffRef(n, n - 1) = Scalar(0);
m_matT.coeffRef(n, n) = Scalar(1);
for (Index i = n - 2; i >= 0; i--)
{
Scalar ra = m_matT.row(i).segment(l, n - l + 1).dot(m_matT.col(n - 1).segment(l, n - l + 1));
Scalar sa = m_matT.row(i).segment(l, n - l + 1).dot(m_matT.col(n).segment(l, n - l + 1));
Scalar w = m_matT.coeff(i, i) - p;
if (m_eivalues.coeff(i).imag() < Scalar(0))
{
lastw = w;
lastra = ra;
lastsa = sa;
}
else
{
l = i;
if (m_eivalues.coeff(i).imag() == Scalar(0))
{
Complex cc = Complex(-ra, -sa) / Complex(w, q);
m_matT.coeffRef(i, n - 1) = Eigen::numext::real(cc);
m_matT.coeffRef(i, n) = Eigen::numext::imag(cc);
}
else
{
// Solve complex equations
Scalar x = m_matT.coeff(i, i + 1);
Scalar y = m_matT.coeff(i + 1, i);
Scalar vr = (m_eivalues.coeff(i).real() - p) * (m_eivalues.coeff(i).real() - p) + m_eivalues.coeff(i).imag() * m_eivalues.coeff(i).imag() - q * q;
Scalar vi = (m_eivalues.coeff(i).real() - p) * Scalar(2) * q;
if ((vr == Scalar(0)) && (vi == Scalar(0)))
vr = eps * norm * (abs(w) + abs(q) + abs(x) + abs(y) + abs(lastw));
Complex cc = Complex(x * lastra - lastw * ra + q * sa, x * lastsa - lastw * sa - q * ra) / Complex(vr, vi);
m_matT.coeffRef(i, n - 1) = Eigen::numext::real(cc);
m_matT.coeffRef(i, n) = Eigen::numext::imag(cc);
if (abs(x) > (abs(lastw) + abs(q)))
{
m_matT.coeffRef(i + 1, n - 1) = (-ra - w * m_matT.coeff(i, n - 1) + q * m_matT.coeff(i, n)) / x;
m_matT.coeffRef(i + 1, n) = (-sa - w * m_matT.coeff(i, n) - q * m_matT.coeff(i, n - 1)) / x;
}
else
{
cc = Complex(-lastra - y * m_matT.coeff(i, n - 1), -lastsa - y * m_matT.coeff(i, n)) / Complex(lastw, q);
m_matT.coeffRef(i + 1, n - 1) = Eigen::numext::real(cc);
m_matT.coeffRef(i + 1, n) = Eigen::numext::imag(cc);
}
}
// Overflow control
Scalar t = (std::max)(abs(m_matT.coeff(i, n - 1)), abs(m_matT.coeff(i, n)));
if ((eps * t) * t > Scalar(1))
m_matT.block(i, n - 1, size - i, 2) /= t;
}
}
// We handled a pair of complex conjugate eigenvalues, so need to skip them both
n--;
}
}
// Back transformation to get eigenvectors of original matrix
Vector m_tmp(size);
for (Index j = size - 1; j >= 0; j--)
{
m_tmp.noalias() = m_eivec.leftCols(j + 1) * m_matT.col(j).segment(0, j + 1);
m_eivec.col(j) = m_tmp;
}
}
public:
UpperHessenbergEigen() :
m_n(0), m_computed(false)
{}
UpperHessenbergEigen(ConstGenericMatrix& mat) :
m_n(mat.rows()), m_computed(false)
{
compute(mat);
}
void compute(ConstGenericMatrix& mat)
{
using std::abs;
using std::sqrt;
if (mat.rows() != mat.cols())
throw std::invalid_argument("UpperHessenbergEigen: matrix must be square");
m_n = mat.rows();
// Scale matrix prior to the Schur decomposition
const Scalar scale = mat.cwiseAbs().maxCoeff();
// Reduce to real Schur form
m_schur.compute(mat / scale);
m_schur.swap_T(m_matT);
m_schur.swap_U(m_eivec);
// Compute eigenvalues from matT
m_eivalues.resize(m_n);
Index i = 0;
while (i < m_n)
{
// Real eigenvalue
if (i == m_n - 1 || m_matT.coeff(i + 1, i) == Scalar(0))
{
m_eivalues.coeffRef(i) = m_matT.coeff(i, i);
++i;
}
else // Complex eigenvalues
{
Scalar p = Scalar(0.5) * (m_matT.coeff(i, i) - m_matT.coeff(i + 1, i + 1));
Scalar z;
// Compute z = sqrt(abs(p * p + m_matT.coeff(i+1, i) * m_matT.coeff(i, i+1)));
// without overflow
{
Scalar t0 = m_matT.coeff(i + 1, i);
Scalar t1 = m_matT.coeff(i, i + 1);
Scalar maxval = (std::max)(abs(p), (std::max)(abs(t0), abs(t1)));
t0 /= maxval;
t1 /= maxval;
Scalar p0 = p / maxval;
z = maxval * sqrt(abs(p0 * p0 + t0 * t1));
}
m_eivalues.coeffRef(i) = Complex(m_matT.coeff(i + 1, i + 1) + p, z);
m_eivalues.coeffRef(i + 1) = Complex(m_matT.coeff(i + 1, i + 1) + p, -z);
i += 2;
}
}
// Compute eigenvectors
doComputeEigenvectors();
// Scale eigenvalues back
m_eivalues *= scale;
m_computed = true;
}
const ComplexVector& eigenvalues() const
{
if (!m_computed)
throw std::logic_error("UpperHessenbergEigen: need to call compute() first");
return m_eivalues;
}
ComplexMatrix eigenvectors()
{
using std::abs;
if (!m_computed)
throw std::logic_error("UpperHessenbergEigen: need to call compute() first");
Index n = m_eivec.cols();
ComplexMatrix matV(n, n);
for (Index j = 0; j < n; ++j)
{
// imaginary part of real eigenvalue is already set to exact zero
if (Eigen::numext::imag(m_eivalues.coeff(j)) == Scalar(0) || j + 1 == n)
{
// we have a real eigen value
matV.col(j) = m_eivec.col(j).template cast<Complex>();
matV.col(j).normalize();
}
else
{
// we have a pair of complex eigen values
for (Index i = 0; i < n; ++i)
{
matV.coeffRef(i, j) = Complex(m_eivec.coeff(i, j), m_eivec.coeff(i, j + 1));
matV.coeffRef(i, j + 1) = Complex(m_eivec.coeff(i, j), -m_eivec.coeff(i, j + 1));
}
matV.col(j).normalize();
matV.col(j + 1).normalize();
++j;
}
}
return matV;
}
};
} // namespace Spectra
#endif // SPECTRA_UPPER_HESSENBERG_EIGEN_H