helper.h

#ifndef LINEARALGEBRA_SRC_MOLPRO_LINALG_ITERATIVESOLVER_HELPER_H_
#define LINEARALGEBRA_SRC_MOLPRO_LINALG_ITERATIVESOLVER_HELPER_H_
#include <complex>
#include <cstddef>
#include <limits>
#include <list>
#include <molpro/iostream.h>
#include <molpro/linalg/array/Span.h>
#include <molpro/linalg/scalar_traits.h>
#include <span>
#include <type_traits>
#include <vector>
 
namespace molpro::linalg::itsolv {
 
// Scalar traits shared with molpro::linalg::array, re-exported here for backwards compatibility
using molpro::linalg::is_complex;
using molpro::linalg::precision_scaled;
using molpro::linalg::real_type;
using molpro::linalg::real_type_t;
 
template <typename T>
struct SVD {
  using value_type = T;
  value_type value;
  std::vector<value_type> u; 
  std::vector<value_type> v; 
};
 
int eigensolver_lapacke_dsyev(std::span<const double> matrix, std::span<double> eigenvectors,
                              std::span<double> eigenvalues, const size_t dimension);
 
std::list<SVD<double>> eigensolver_lapacke_dsyev(size_t dimension, std::span<const double> matrix);
 
template <typename value_type>
size_t get_rank(std::span<const value_type> eigenvalues, value_type threshold);
 
template <typename value_type>
size_t get_rank(std::list<SVD<value_type>> svd_system, value_type threshold);
 
template <typename value_type>
size_t get_rank(const std::vector<value_type>& eigenvalues, value_type threshold) {
  return get_rank<value_type>(std::span<const value_type>{eigenvalues.data(), eigenvalues.size()}, threshold);
}
 
template <typename value_type, typename std::enable_if_t<!is_complex<value_type>{}, std::nullptr_t> = nullptr>
std::list<SVD<value_type>> svd_system(size_t nrows, size_t ncols, const array::Span<value_type>& m,
                                      real_type_t<value_type> threshold, bool hermitian = false,
                                      bool reduce_to_rank = false);
template <typename value_type, typename std::enable_if_t<is_complex<value_type>{}, int> = 0>
std::list<SVD<value_type>> svd_system(size_t nrows, size_t ncols, const array::Span<value_type>& m,
                                      real_type_t<value_type> threshold, bool hermitian = false,
                                      bool reduce_to_rank = false);
 
template <typename value_type>
void printMatrix(const std::vector<value_type>&, size_t rows, size_t cols, std::string title = "",
                 std::ostream& s = molpro::cout);
 
template <typename value_type, typename std::enable_if_t<is_complex<value_type>{}, int> = 0>
void eigenproblem(std::vector<value_type>& eigenvectors, std::vector<value_type>& eigenvalues,
                  const std::vector<value_type>& matrix, const std::vector<value_type>& metric, size_t dimension,
                  bool hermitian, real_type_t<value_type> svdThreshold, int verbosity);
 
template <typename value_type, typename std::enable_if_t<!is_complex<value_type>{}, std::nullptr_t> = nullptr>
void eigenproblem(std::vector<value_type>& eigenvectors, std::vector<value_type>& eigenvalues,
                  const std::vector<value_type>& matrix, const std::vector<value_type>& metric, size_t dimension,
                  bool hermitian, real_type_t<value_type> svdThreshold, int verbosity,
                  std::vector<std::pair<std::size_t, value_type>> *imag_eval_parts = nullptr);
 
template <typename value_type, typename std::enable_if_t<is_complex<value_type>{}, int> = 0>
void solve_LinearEquations(std::vector<value_type>& solution, std::vector<value_type>& eigenvalues,
                           const std::vector<value_type>& matrix, const std::vector<value_type>& metric,
                           const std::vector<value_type>& rhs, size_t dimension, size_t nroot,
                           real_type_t<value_type> augmented_hessian, real_type_t<value_type> svdThreshold,
                           int verbosity);
 
template <typename value_type, typename std::enable_if_t<!is_complex<value_type>{}, std::nullptr_t> = nullptr>
void solve_LinearEquations(std::vector<value_type>& solution, std::vector<value_type>& eigenvalues,
                           const std::vector<value_type>& matrix, const std::vector<value_type>& metric,
                           const std::vector<value_type>& rhs, size_t dimension, size_t nroot,
                           real_type_t<value_type> augmented_hessian, real_type_t<value_type> svdThreshold,
                           int verbosity);
 
template <typename value_type, typename std::enable_if_t<is_complex<value_type>{}, int> = 0>
void solve_DIIS(std::vector<value_type>& solution, const std::vector<value_type>& matrix, size_t dimension,
                real_type_t<value_type> svdThreshold, int verbosity = 0);
template <typename value_type, typename std::enable_if_t<!is_complex<value_type>{}, std::nullptr_t> = nullptr>
void solve_DIIS(std::vector<value_type>& solution, const std::vector<value_type>& matrix, size_t dimension,
                real_type_t<value_type> svdThreshold, int verbosity = 0);
 
/*
 * Explicit instantiation of double type
 */
 
extern template void printMatrix<double>(const std::vector<double>&, size_t rows, size_t cols, std::string title,
                                         std::ostream& s);
 
extern template size_t get_rank<double>(std::span<const double> eigenvalues, double threshold);
 
extern template std::list<SVD<double>> svd_system(size_t nrows, size_t ncols, const array::Span<double>& m,
                                                  double threshold, bool hermitian, bool reduce_to_rank);
 
extern template void eigenproblem<double>(std::vector<double>& eigenvectors, std::vector<double>& eigenvalues,
                                          const std::vector<double>& matrix, const std::vector<double>& metric,
                                          const size_t dimension, bool hermitian, double svdThreshold, int verbosity,
                                          std::vector<std::pair<std::size_t, double>> *imag_eval_parts);
 
extern template void solve_LinearEquations<double>(std::vector<double>& solution, std::vector<double>& eigenvalues,
                                                   const std::vector<double>& matrix, const std::vector<double>& metric,
                                                   const std::vector<double>& rhs, size_t dimension, size_t nroot,
                                                   double augmented_hessian, double svdThreshold, int verbosity);
 
extern template void solve_DIIS<double>(std::vector<double>& solution, const std::vector<double>& matrix,
                                        const size_t dimension, double svdThreshold, int verbosity);
 
/*
 * Explicit instantiation of long double type
 *
 * LAPACK has no kernels for this precision, so these exercise the Eigen branch of the dispatch.
 */
 
extern template void printMatrix<long double>(const std::vector<long double>&, size_t rows, size_t cols,
                                              std::string title, std::ostream& s);
 
extern template size_t get_rank<long double>(std::span<const long double> eigenvalues, long double threshold);
 
extern template std::list<SVD<long double>> svd_system(size_t nrows, size_t ncols, const array::Span<long double>& m,
                                                       long double threshold, bool hermitian, bool reduce_to_rank);
 
extern template void eigenproblem<long double>(std::vector<long double>& eigenvectors,
                                               std::vector<long double>& eigenvalues,
                                               const std::vector<long double>& matrix,
                                               const std::vector<long double>& metric, const size_t dimension,
                                               bool hermitian, long double svdThreshold, int verbosity,
                                               std::vector<std::pair<std::size_t, long double>> *imag_eval_parts);
 
extern template void solve_LinearEquations<long double>(
    std::vector<long double>& solution, std::vector<long double>& eigenvalues, const std::vector<long double>& matrix,
    const std::vector<long double>& metric, const std::vector<long double>& rhs, size_t dimension, size_t nroot,
    long double augmented_hessian, long double svdThreshold, int verbosity);
 
extern template void solve_DIIS<long double>(std::vector<long double>& solution, const std::vector<long double>& matrix,
                                             const size_t dimension, long double svdThreshold, int verbosity);
 
/*
 * Explicit instantiation of std::complex<double> type
 */
extern template void printMatrix<std::complex<double>>(const std::vector<std::complex<double>>&, size_t rows,
                                                       size_t cols, std::string title, std::ostream& s);
 
extern template std::list<SVD<std::complex<double>>> svd_system(size_t nrows, size_t ncols,
                                                                const array::Span<std::complex<double>>& m,
                                                                double threshold, bool hermitian, bool reduce_to_rank);
 
extern template void eigenproblem<std::complex<double>>(std::vector<std::complex<double>>& eigenvectors,
                                                        std::vector<std::complex<double>>& eigenvalues,
                                                        const std::vector<std::complex<double>>& matrix,
                                                        const std::vector<std::complex<double>>& metric,
                                                        const size_t dimension, bool hermitian, double svdThreshold,
                                                        int verbosity);
 
extern template void solve_LinearEquations<std::complex<double>>(
    std::vector<std::complex<double>>& solution, std::vector<std::complex<double>>& eigenvalues,
    const std::vector<std::complex<double>>& matrix, const std::vector<std::complex<double>>& metric,
    const std::vector<std::complex<double>>& rhs, size_t dimension, size_t nroot, double augmented_hessian,
    double svdThreshold, int verbosity);
 
extern template void solve_DIIS<std::complex<double>>(std::vector<std::complex<double>>& solution,
                                                      const std::vector<std::complex<double>>& matrix,
                                                      const size_t dimension, double svdThreshold, int verbosity);
} // namespace molpro::linalg::itsolv
#endif // LINEARALGEBRA_SRC_MOLPRO_LINALG_ITERATIVESOLVER_HELPER_H_