28 Numerics library [numerics]

28.9 Basic linear algebra algorithms [linalg]

28.9.5 Tag classes [linalg.tags]

28.9.5.3 Diagonal tags [linalg.tags.diagonal]

struct implicit_unit_diagonal_t {
  explicit implicit_unit_diagonal_t() = default;
};
inline constexpr implicit_unit_diagonal_t
  implicit_unit_diagonal{};

struct explicit_diagonal_t {
  explicit explicit_diagonal_t() = default;
};
inline constexpr explicit_diagonal_t explicit_diagonal{};

These tag classes specify whether algorithms access the matrix's diagonal entries, and if not, then how algorithms interpret the matrix's implicitly represented diagonal values.

The implicit_unit_diagonal_t tag indicates that an implicit unit diagonal is to be assumed ([linalg.general]).

The explicit_diagonal_t tag indicates that an explicit diagonal is used ([linalg.general]).