[linalg.tags.triangle]

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struct upper_triangle_t {
  explicit upper_triangle_t() = default;
};
inline constexpr upper_triangle_t upper_triangle{};

struct lower_triangle_t {
  explicit lower_triangle_t() = default;
};
inline constexpr lower_triangle_t lower_triangle{};

These tag classes specify whether algorithms and other users of a matrix (represented as an mdspan) access the upper triangle (upper_triangle_t) or lower triangle (lower_triangle_t) of the matrix (see also [linalg.general]).

This is also subject to the restrictions of implicit_unit_diagonal_t if that tag is also used as a function argument; see below.

29 Numerics library [numerics]

29.9 Basic linear algebra algorithms [linalg]

29.9.5 Tag classes [linalg.tags]

29.9.5.2 Triangle tags [linalg.tags.triangle]