eigenvalues_sym.hpp

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#ifndef STAN_MATH_PRIM_FUN_EIGENVALUES_SYM_HPP
#define STAN_MATH_PRIM_FUN_EIGENVALUES_SYM_HPP
 
#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/err.hpp>
#include <stan/math/prim/fun/Eigen.hpp>
 
namespace stan {
namespace math {
 
template <typename EigMat, require_eigen_matrix_dynamic_t<EigMat>* = nullptr,
          require_not_st_var<EigMat>* = nullptr>
inline Eigen::Matrix<value_type_t<EigMat>, -1, 1> eigenvalues_sym(
    const EigMat& m) {
  if (unlikely(m.size() == 0)) {
    return Eigen::Matrix<value_type_t<EigMat>, -1, 1>(0, 1);
  }
  using PlainMat = plain_type_t<EigMat>;
  const PlainMat& m_eval = m;
  check_symmetric("eigenvalues_sym", "m", m_eval);
 
  Eigen::SelfAdjointEigenSolver<PlainMat> solver(m_eval,
                                                 Eigen::EigenvaluesOnly);
  return solver.eigenvalues();
}
 
}  // namespace math
}  // namespace stan
 
#endif