28 Numerics library [numerics]

28.9 Basic linear algebra algorithms [linalg]

28.9.6 Layouts for packed matrix types [linalg.layout.packed]

28.9.6.3 Observers [linalg.layout.packed.obs]

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constexpr index_type required_span_size() const noexcept;
1
#
Returns: extents_.extent(0) * (extents_.extent(0) + 1)/2.
[Note 1: 
For example, a 5 x 5 packed matrix only stores 15 matrix elements.
— end note]
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template<class Index0, class Index1> constexpr index_type operator() (Index0 ind0, Index1 ind1) const noexcept;
2
#
Constraints:
  • (2.1)
    is_convertible_v<Index0, index_type> is true,
  • (2.2)
    is_convertible_v<Index1, index_type> is true,
  • (2.3)
    is_nothrow_constructible_v<index_type, Index0> is true, and
  • (2.4)
    is_nothrow_constructible_v<index_type, Index1> is true.
3
#
Let i be extents_type​::​index-cast(ind0), and let j be extents_type​::​index-cast(ind1).
4
#
Preconditions: i, j is a multidimensional index in extents_ ([mdspan.overview]).
5
#
Returns: Let N be extents_.extent(0).
Then
  • (5.1)
    (*this)(j, i) if i > j is true; otherwise
  • (5.2)
    i + j * (j + 1)/2 if is_same_v<StorageOrder, column_major_t> && is_same_v<Triangle, upper_triangle_t> is true or is_same_v<StorageOrder, row_major_t> && is_same_v<Triangle, lower_triangle_t> is true; otherwise
  • (5.3)
    j + N * i - i * (i + 1)/2.
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constexpr index_type stride(rank_type r) const noexcept;
6
#
Preconditions:
  • (6.1)
    is_strided() is true, and
  • (6.2)
    r < extents_type​::​rank() is true.
7
#
Returns: 1.
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template<class OtherExtents> friend constexpr bool operator==(const mapping& x, const mapping<OtherExtents>& y) noexcept;
8
#
Effects: Equivalent to: return x.extents() == y.extents();