util.h

#ifndef LINEARALGEBRA_SRC_MOLPRO_LINALG_ITSOLV_SUBSPACE_UTIL_H
#define LINEARALGEBRA_SRC_MOLPRO_LINALG_ITSOLV_SUBSPACE_UTIL_H
#include <limits>
#include <molpro/linalg/itsolv/ArrayHandlers.h>
#include <molpro/linalg/itsolv/subspace/Matrix.h>
#include <molpro/linalg/itsolv/wrap.h>
 
namespace molpro::linalg::itsolv::subspace::util {
namespace detail {
 
template <typename T1, typename T2, typename... Ts>
struct is_one_of {
  static constexpr bool value = std::is_same<T1, T2>::value || is_one_of<T1, Ts...>::value;
};
 
template <typename T1, typename T2>
struct is_one_of<T1, T2> {
  static constexpr bool value = std::is_same<T1, T2>::value;
};
 
template <class R, class Q, class Z, class W, bool = is_one_of<Z, R, Q>::value&& is_one_of<W, R, Q>::value,
          bool = std::is_same<R, Z>::value, bool = std::is_same<W, Q>::value>
struct Overlap {};
 
template <class R, class Q, class Z, class W>
struct Overlap<R, Q, Z, W, true, true, true> {
  using value_type = typename array::ArrayHandler<Z, W>::value_type;
  static Matrix<value_type> _(const CVecRef<R>& left, const CVecRef<Q>& right, array::ArrayHandler<Z, W>& handler) {
    return handler.gemm_inner(left, right);
  }
};
 
template <class R, class Q, class Z, class W>
struct Overlap<R, Q, Z, W, true, false, false> {
  using value_type = typename array::ArrayHandler<Z, W>::value_type;
  static Matrix<value_type> _(const CVecRef<R>& left, const CVecRef<Q>& right, array::ArrayHandler<Z, W>& handler) {
    // gemm_inner(right, left)(i, j) = <right_i|left_j>, and <left_j|right_i> is its conjugate
    auto mat = handler.gemm_inner(right, left);
    auto m = Matrix<value_type>({left.size(), right.size()});
    conjugate_transpose_copy(m, mat);
    return m;
  }
};
 
template <class R, class Q, class Z, class W>
constexpr bool Z_and_W_are_one_of_R_and_Q = detail::is_one_of<Z, R, Q>::value&& detail::is_one_of<W, R, Q>::value;
} // namespace detail
 
template <class R, class Q, class Z, class W>
auto overlap(const CVecRef<R>& left, const CVecRef<Q>& right, array::ArrayHandler<Z, W>& handler)
    -> std::enable_if_t<detail::Z_and_W_are_one_of_R_and_Q<R, Q, Z, W>,
                        Matrix<typename array::ArrayHandler<Z, W>::value_type>> {
  return detail::Overlap<R, Q, Z, W>::_(left, right, handler);
}
 
template <class R>
Matrix<typename array::ArrayHandler<R, R>::value_type> overlap(const CVecRef<R>& params,
                                                               array::ArrayHandler<R, R>& handler) {
  auto m = Matrix<typename array::ArrayHandler<R, R>::value_type>({params.size(), params.size()});
  for (size_t i = 0; i < m.rows(); ++i)
    for (size_t j = 0; j <= i; ++j) {
      m(i, j) = handler.dot(params[i], params[j]);
      m(j, i) = conjugate(m(i, j)); // the matrix is hermitian, which for a real element type is symmetric
    }
  return m;
}
 
template <typename T>
void matrix_symmetrize(Matrix<T>& mat) {
  assert(mat.rows() == mat.cols() && "must be a square matrix");
  for (size_t i = 0; i < mat.rows(); ++i)
    for (size_t j = 0; j < i; ++j) {
      mat(i, j) = T(0.5) * (mat(i, j) + conjugate(mat(j, i)));
      mat(j, i) = conjugate(mat(i, j));
    }
}
 
template <typename T>
typename Matrix<T>::coord_type max_element_index(const std::list<size_t>& rows, const std::list<size_t>& cols,
                                                 const Matrix<T>& mat) {
  auto max_el = std::numeric_limits<T>::lowest();
  auto ind = typename Matrix<T>::coord_type{0, 0};
  for (auto i : rows) {
    for (auto j : cols) {
      if (mat(i, j) > max_el) {
        max_el = mat(i, j);
        ind = {i, j};
      }
    }
  }
  return ind;
}
 
template <typename Slice>
std::vector<size_t> eye_order(const Slice& mat) {
  auto dim = mat.dimensions();
  auto rows = std::list<size_t>{};
  auto cols = std::list<size_t>{};
  for (size_t i = 0; i < dim.first; ++i) {
    rows.emplace_back(i);
    cols.emplace_back(i);
  }
  auto order = std::vector<size_t>(dim.first);
  size_t i, j;
  while (!rows.empty() && !cols.empty()) {
    std::tie(i, j) = max_element_index(rows, cols, mat);
    order.at(j) = i;
    auto it_row = std::find(begin(rows), end(rows), i);
    auto it_col = std::find(begin(cols), end(cols), j);
    rows.erase(it_row);
    cols.erase(it_col);
  }
  return order;
}
 
} // namespace molpro::linalg::itsolv::subspace::util
 
#endif // LINEARALGEBRA_SRC_MOLPRO_LINALG_ITSOLV_SUBSPACE_UTIL_H