legacyArray.hpp

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//
// Copyright (c) 2025, University of Colorado Denver. All rights reserved.
//
// This file is part of <T>LAPACK.
// <T>LAPACK is free software: you can redistribute it and/or modify it under
// the terms of the BSD 3-Clause license. See the accompanying LICENSE file.
 
#ifndef TLAPACK_LEGACYARRAY_HH
#define TLAPACK_LEGACYARRAY_HH
 
#include <cassert>
 
#include "tlapack/LegacyBandedMatrix.hpp"
#include "tlapack/LegacyMatrix.hpp"
#include "tlapack/LegacyVector.hpp"
#include "tlapack/base/arrayTraits.hpp"
#include "tlapack/plugins/stdvector.hpp"
 
namespace tlapack {
 
// -----------------------------------------------------------------------------
// Helpers
 
namespace traits {
    namespace internal {
        template <typename T, class idx_t, Layout L>
        std::true_type is_legacy_type_f(const LegacyMatrix<T, idx_t, L>*);
 
        template <typename T, class idx_t, class int_t, Direction D>
        std::true_type is_legacy_type_f(
            const LegacyVector<T, idx_t, int_t, D>*);
 
        std::false_type is_legacy_type_f(const void*);
    }  // namespace internal
 
    template <class T>
    constexpr bool is_legacy_type =
        decltype(internal::is_legacy_type_f(std::declval<T*>()))::value;
}  // namespace traits
 
// -----------------------------------------------------------------------------
// Data traits
 
namespace traits {
    template <typename T, class idx_t, Layout L>
    struct layout_trait<LegacyMatrix<T, idx_t, L>, int> {
        static constexpr Layout value = L;
    };
 
    template <typename T, class idx_t, typename int_t, Direction D>
    struct layout_trait<LegacyVector<T, idx_t, int_t, D>, int> {
        static constexpr Layout value = Layout::Strided;
    };
 
    template <class T, class idx_t, typename int_t, Direction D>
    struct real_type_traits<LegacyVector<T, idx_t, int_t, D>, int> {
        using type = LegacyVector<real_type<T>, idx_t, int_t, D>;
    };
 
    template <typename T, class idx_t, Layout layout>
    struct real_type_traits<LegacyMatrix<T, idx_t, layout>, int> {
        using type = LegacyMatrix<real_type<T>, idx_t, layout>;
    };
 
    template <class T, class idx_t, typename int_t, Direction D>
    struct complex_type_traits<LegacyVector<T, idx_t, int_t, D>, int> {
        using type = LegacyVector<complex_type<T>, idx_t, int_t, D>;
    };
 
    template <typename T, class idx_t, Layout layout>
    struct complex_type_traits<LegacyMatrix<T, idx_t, layout>, int> {
        using type = LegacyMatrix<complex_type<T>, idx_t, layout>;
    };
 
    template <class U, class idx_t, Layout layout>
    struct CreateFunctor<LegacyMatrix<U, idx_t, layout>, int> {
        template <class T>
        constexpr auto operator()(std::vector<T>& v, idx_t m, idx_t n) const
        {
            assert(m >= 0 && n >= 0);
            v.resize(m * n);  // Allocates space in memory
            return LegacyMatrix<T, idx_t, layout>(m, n, v.data());
        }
    };
 
    template <class U, class idx_t, Layout layout, int m, int n>
    struct CreateStaticFunctor<LegacyMatrix<U, idx_t, layout>, m, n, int> {
        static_assert(m >= 0 && n >= 0);
 
        template <typename T>
        constexpr auto operator()(T* v) const
        {
            return LegacyMatrix<T, idx_t, layout>(m, n, v);
        }
    };
 
    template <class U, class idx_t, typename int_t, Direction D>
    struct CreateFunctor<LegacyVector<U, idx_t, int_t, D>, int> {
        template <class T>
        constexpr auto operator()(std::vector<T>& v, idx_t n) const
        {
            assert(n >= 0);
            v.resize(n);  // Allocates space in memory
            return LegacyVector<T, idx_t, int_t, D>(n, v.data());
        }
    };
 
    template <class U, class idx_t, typename int_t, Direction D, int n>
    struct CreateStaticFunctor<LegacyVector<U, idx_t, int_t, D>, n, -1, int> {
        static_assert(n >= 0);
 
        template <typename T>
        constexpr auto operator()(T* v) const
        {
            return LegacyVector<T, idx_t>(n, v);
        }
    };
}  // namespace traits
 
// -----------------------------------------------------------------------------
// Data descriptors
 
// Number of rows of LegacyMatrix
template <typename T, class idx_t, Layout layout>
constexpr auto nrows(const LegacyMatrix<T, idx_t, layout>& A) noexcept
{
    return A.m;
}
 
// Number of columns of LegacyMatrix
template <typename T, class idx_t, Layout layout>
constexpr auto ncols(const LegacyMatrix<T, idx_t, layout>& A) noexcept
{
    return A.n;
}
 
// Size of LegacyMatrix
template <typename T, class idx_t, Layout layout>
constexpr auto size(const LegacyMatrix<T, idx_t, layout>& A) noexcept
{
    return A.m * A.n;
}
 
// Size of LegacyVector
template <typename T, class idx_t, typename int_t, Direction direction>
constexpr auto size(const LegacyVector<T, idx_t, int_t, direction>& x) noexcept
{
    return x.n;
}
 
// Number of rows of LegacyBandedMatrix
template <typename T, class idx_t>
constexpr auto nrows(const LegacyBandedMatrix<T, idx_t>& A) noexcept
{
    return A.m;
}
 
// Number of columns of LegacyBandedMatrix
template <typename T, class idx_t>
constexpr auto ncols(const LegacyBandedMatrix<T, idx_t>& A) noexcept
{
    return A.n;
}
 
// Size of LegacyBandedMatrix
template <typename T, class idx_t>
constexpr auto size(const LegacyBandedMatrix<T, idx_t>& A) noexcept
{
    return A.m * A.n;
}
 
// Lowerband of LegacyBandedMatrix
template <typename T, class idx_t>
constexpr auto lowerband(const LegacyBandedMatrix<T, idx_t>& A) noexcept
{
    return A.kl;
}
 
// Upperband of LegacyBandedMatrix
template <typename T, class idx_t>
constexpr auto upperband(const LegacyBandedMatrix<T, idx_t>& A) noexcept
{
    return A.ku;
}
 
// -----------------------------------------------------------------------------
// Block operations for const LegacyMatrix
 
#define isSlice(SliceSpec) !std::is_convertible<SliceSpec, idx_t>::value
 
// Slice LegacyMatrix
template <
    typename T,
    class idx_t,
    Layout layout,
    class SliceSpecRow,
    class SliceSpecCol,
    typename std::enable_if<isSlice(SliceSpecRow) && isSlice(SliceSpecCol),
                            int>::type = 0>
constexpr auto slice(const LegacyMatrix<T, idx_t, layout>& A,
                     SliceSpecRow&& rows,
                     SliceSpecCol&& cols) noexcept
{
    assert((rows.first >= 0 and (idx_t) rows.first < nrows(A)) ||
           rows.first == rows.second);
    assert(rows.second >= 0 and (idx_t) rows.second <= nrows(A));
    assert(rows.first <= rows.second);
    assert((cols.first >= 0 and (idx_t) cols.first < ncols(A)) ||
           cols.first == cols.second);
    assert(cols.second >= 0 and (idx_t) cols.second <= ncols(A));
    assert(cols.first <= cols.second);
    return LegacyMatrix<const T, idx_t, layout>(
        rows.second - rows.first, cols.second - cols.first,
        (layout == Layout::ColMajor) ? &A.ptr[rows.first + cols.first * A.ldim]
                                     : &A.ptr[rows.first * A.ldim + cols.first],
        A.ldim);
}
 
#undef isSlice
 
// Slice LegacyMatrix over a single row
template <typename T, class idx_t, Layout layout, class SliceSpecCol>
constexpr auto slice(const LegacyMatrix<T, idx_t, layout>& A,
                     size_type<LegacyMatrix<T, idx_t, layout>> rowIdx,
                     SliceSpecCol&& cols) noexcept
{
    assert((cols.first >= 0 and (idx_t) cols.first < ncols(A)) ||
           cols.first == cols.second);
    assert(cols.second >= 0 and (idx_t) cols.second <= ncols(A));
    assert(cols.first <= cols.second);
    assert(rowIdx >= 0 and rowIdx < nrows(A));
    return LegacyVector<const T, idx_t, idx_t>(
        cols.second - cols.first,
        (layout == Layout::ColMajor) ? &A.ptr[rowIdx + cols.first * A.ldim]
                                     : &A.ptr[rowIdx * A.ldim + cols.first],
        layout == Layout::ColMajor ? A.ldim : 1);
}
 
// Slice LegacyMatrix over a single column
template <typename T, class idx_t, Layout layout, class SliceSpecRow>
constexpr auto slice(const LegacyMatrix<T, idx_t, layout>& A,
                     SliceSpecRow&& rows,
                     size_type<LegacyMatrix<T, idx_t, layout>> colIdx) noexcept
{
    assert((rows.first >= 0 and (idx_t) rows.first < nrows(A)) ||
           rows.first == rows.second);
    assert(rows.second >= 0 and (idx_t) rows.second <= nrows(A));
    assert(rows.first <= rows.second);
    assert(colIdx >= 0 and colIdx < ncols(A));
    return LegacyVector<const T, idx_t, idx_t>(
        rows.second - rows.first,
        (layout == Layout::ColMajor) ? &A.ptr[rows.first + colIdx * A.ldim]
                                     : &A.ptr[rows.first * A.ldim + colIdx],
        layout == Layout::RowMajor ? A.ldim : 1);
}
 
// Get rows of LegacyMatrix
template <typename T, class idx_t, Layout layout, class SliceSpec>
constexpr auto rows(const LegacyMatrix<T, idx_t, layout>& A,
                    SliceSpec&& rows) noexcept
{
    assert((rows.first >= 0 and (idx_t) rows.first < nrows(A)) ||
           rows.first == rows.second);
    assert(rows.second >= 0 and (idx_t) rows.second <= nrows(A));
    assert(rows.first <= rows.second);
    return LegacyMatrix<const T, idx_t, layout>(
        rows.second - rows.first, A.n,
        (layout == Layout::ColMajor) ? &A.ptr[rows.first]
                                     : &A.ptr[rows.first * A.ldim],
        A.ldim);
}
 
// Get a row of a column-major LegacyMatrix
template <typename T, class idx_t>
constexpr auto row(const LegacyMatrix<T, idx_t>& A,
                   size_type<LegacyMatrix<T, idx_t>> rowIdx) noexcept
{
    assert(rowIdx >= 0 and rowIdx < nrows(A));
    return LegacyVector<const T, idx_t, idx_t>(A.n, &A.ptr[rowIdx], A.ldim);
}
 
// Get a row of a row-major LegacyMatrix
template <typename T, class idx_t>
constexpr auto row(
    const LegacyMatrix<T, idx_t, Layout::RowMajor>& A,
    size_type<LegacyMatrix<T, idx_t, Layout::RowMajor>> rowIdx) noexcept
{
    assert(rowIdx >= 0 and rowIdx < nrows(A));
    return LegacyVector<const T, idx_t>(A.n, &A.ptr[rowIdx * A.ldim]);
}
 
// Get columns of LegacyMatrix
template <typename T, class idx_t, Layout layout, class SliceSpec>
constexpr auto cols(const LegacyMatrix<T, idx_t, layout>& A,
                    SliceSpec&& cols) noexcept
{
    assert((cols.first >= 0 and (idx_t) cols.first < ncols(A)) ||
           cols.first == cols.second);
    assert(cols.second >= 0 and (idx_t) cols.second <= ncols(A));
    assert(cols.first <= cols.second);
    return LegacyMatrix<const T, idx_t, layout>(
        A.m, cols.second - cols.first,
        (layout == Layout::ColMajor) ? &A.ptr[cols.first * A.ldim]
                                     : &A.ptr[cols.first],
        A.ldim);
}
 
// Get a column of a column-major LegacyMatrix
template <typename T, class idx_t>
constexpr auto col(const LegacyMatrix<T, idx_t>& A,
                   size_type<LegacyMatrix<T, idx_t>> colIdx) noexcept
{
    assert(colIdx >= 0 and colIdx < ncols(A));
    return LegacyVector<const T, idx_t>(A.m, &A.ptr[colIdx * A.ldim]);
}
 
// Get a column of a row-major LegacyMatrix
template <typename T, class idx_t>
constexpr auto col(
    const LegacyMatrix<T, idx_t, Layout::RowMajor>& A,
    size_type<LegacyMatrix<T, idx_t, Layout::RowMajor>> colIdx) noexcept
{
    assert(colIdx >= 0 and colIdx < ncols(A));
    return LegacyVector<const T, idx_t, idx_t>(A.m, &A.ptr[colIdx], A.ldim);
}
 
// Diagonal of a LegacyMatrix
template <typename T, class idx_t, Layout layout>
constexpr auto diag(const LegacyMatrix<T, idx_t, layout>& A,
                    int diagIdx = 0) noexcept
{
    assert(diagIdx >= 0 || (idx_t)(-diagIdx) < nrows(A));
    assert(diagIdx <= 0 || (idx_t)diagIdx < ncols(A));
    T* ptr =
        (layout == Layout::ColMajor)
            ? ((diagIdx >= 0) ? &A.ptr[diagIdx * A.ldim] : &A.ptr[-diagIdx])
            : ((diagIdx >= 0) ? &A.ptr[diagIdx] : &A.ptr[-diagIdx * A.ldim]);
    idx_t n = (diagIdx >= 0) ? std::min(A.m + diagIdx, A.n) - (idx_t)diagIdx
                             : std::min(A.m, A.n - diagIdx) + (idx_t)diagIdx;
 
    return LegacyVector<const T, idx_t, idx_t>(n, ptr, A.ldim + 1);
}
 
// Transpose view of a LegacyMatrix
template <typename T, class idx_t>
constexpr auto transpose_view(
    const LegacyMatrix<T, idx_t, Layout::ColMajor>& A) noexcept
{
    return LegacyMatrix<const T, idx_t, Layout::RowMajor>(A.n, A.m, A.ptr,
                                                          A.ldim);
}
template <typename T, class idx_t>
constexpr auto transpose_view(
    const LegacyMatrix<T, idx_t, Layout::RowMajor>& A) noexcept
{
    return LegacyMatrix<const T, idx_t, Layout::ColMajor>(A.n, A.m, A.ptr,
                                                          A.ldim);
}
 
// slice LegacyVector
template <typename T,
          class idx_t,
          typename int_t,
          Direction direction,
          class SliceSpec>
constexpr auto slice(const LegacyVector<T, idx_t, int_t, direction>& v,
                     SliceSpec&& rows) noexcept
{
    assert((rows.first >= 0 and (idx_t) rows.first < size(v)) ||
           rows.first == rows.second);
    assert(rows.second >= 0 and (idx_t) rows.second <= size(v));
    assert(rows.first <= rows.second);
    return LegacyVector<const T, idx_t, int_t, direction>(
        rows.second - rows.first, &v.ptr[rows.first * v.inc], v.inc);
}
 
// -----------------------------------------------------------------------------
// Block operations for non-const LegacyMatrix
 
#define isSlice(SliceSpec) !std::is_convertible<SliceSpec, idx_t>::value
 
// Slice LegacyMatrix
template <
    typename T,
    class idx_t,
    Layout layout,
    class SliceSpecRow,
    class SliceSpecCol,
    typename std::enable_if<isSlice(SliceSpecRow) && isSlice(SliceSpecCol),
                            int>::type = 0>
constexpr auto slice(LegacyMatrix<T, idx_t, layout>& A,
                     SliceSpecRow&& rows,
                     SliceSpecCol&& cols) noexcept
{
    assert((rows.first >= 0 and (idx_t) rows.first < nrows(A)) ||
           rows.first == rows.second);
    assert(rows.second >= 0 and (idx_t) rows.second <= nrows(A));
    assert(rows.first <= rows.second);
    assert((cols.first >= 0 and (idx_t) cols.first < ncols(A)) ||
           cols.first == cols.second);
    assert(cols.second >= 0 and (idx_t) cols.second <= ncols(A));
    assert(cols.first <= cols.second);
    return LegacyMatrix<T, idx_t, layout>(
        rows.second - rows.first, cols.second - cols.first,
        (layout == Layout::ColMajor) ? &A.ptr[rows.first + cols.first * A.ldim]
                                     : &A.ptr[rows.first * A.ldim + cols.first],
        A.ldim);
}
 
#undef isSlice
 
// Slice LegacyMatrix over a single row
template <typename T, class idx_t, Layout layout, class SliceSpecCol>
constexpr auto slice(LegacyMatrix<T, idx_t, layout>& A,
                     size_type<LegacyMatrix<T, idx_t, layout>> rowIdx,
                     SliceSpecCol&& cols) noexcept
{
    assert((cols.first >= 0 and (idx_t) cols.first < ncols(A)) ||
           cols.first == cols.second);
    assert(cols.second >= 0 and (idx_t) cols.second <= ncols(A));
    assert(cols.first <= cols.second);
    assert(rowIdx >= 0 and rowIdx < nrows(A));
    return LegacyVector<T, idx_t, idx_t>(
        cols.second - cols.first,
        (layout == Layout::ColMajor) ? &A.ptr[rowIdx + cols.first * A.ldim]
                                     : &A.ptr[rowIdx * A.ldim + cols.first],
        layout == Layout::ColMajor ? A.ldim : 1);
}
 
// Slice LegacyMatrix over a single column
template <typename T, class idx_t, Layout layout, class SliceSpecRow>
constexpr auto slice(LegacyMatrix<T, idx_t, layout>& A,
                     SliceSpecRow&& rows,
                     size_type<LegacyMatrix<T, idx_t, layout>> colIdx) noexcept
{
    assert((rows.first >= 0 and (idx_t) rows.first < nrows(A)) ||
           rows.first == rows.second);
    assert(rows.second >= 0 and (idx_t) rows.second <= nrows(A));
    assert(rows.first <= rows.second);
    assert(colIdx >= 0 and colIdx < ncols(A));
    return LegacyVector<T, idx_t, idx_t>(
        rows.second - rows.first,
        (layout == Layout::ColMajor) ? &A.ptr[rows.first + colIdx * A.ldim]
                                     : &A.ptr[rows.first * A.ldim + colIdx],
        layout == Layout::RowMajor ? A.ldim : 1);
}
 
// Get rows of LegacyMatrix
template <typename T, class idx_t, Layout layout, class SliceSpec>
constexpr auto rows(LegacyMatrix<T, idx_t, layout>& A,
                    SliceSpec&& rows) noexcept
{
    assert((rows.first >= 0 and (idx_t) rows.first < nrows(A)) ||
           rows.first == rows.second);
    assert(rows.second >= 0 and (idx_t) rows.second <= nrows(A));
    assert(rows.first <= rows.second);
    return LegacyMatrix<T, idx_t, layout>(rows.second - rows.first, A.n,
                                          (layout == Layout::ColMajor)
                                              ? &A.ptr[rows.first]
                                              : &A.ptr[rows.first * A.ldim],
                                          A.ldim);
}
 
// Get a row of a column-major LegacyMatrix
template <typename T, class idx_t>
constexpr auto row(LegacyMatrix<T, idx_t>& A,
                   size_type<LegacyMatrix<T, idx_t>> rowIdx) noexcept
{
    assert(rowIdx >= 0 and rowIdx < nrows(A));
    return LegacyVector<T, idx_t, idx_t>(A.n, &A.ptr[rowIdx], A.ldim);
}
 
// Get a row of a row-major LegacyMatrix
template <typename T, class idx_t>
constexpr auto row(
    LegacyMatrix<T, idx_t, Layout::RowMajor>& A,
    size_type<LegacyMatrix<T, idx_t, Layout::RowMajor>> rowIdx) noexcept
{
    assert(rowIdx >= 0 and rowIdx < nrows(A));
    return LegacyVector<T, idx_t>(A.n, &A.ptr[rowIdx * A.ldim]);
}
 
// Get columns of LegacyMatrix
template <typename T, class idx_t, Layout layout, class SliceSpec>
constexpr auto cols(LegacyMatrix<T, idx_t, layout>& A,
                    SliceSpec&& cols) noexcept
{
    assert((cols.first >= 0 and (idx_t) cols.first < ncols(A)) ||
           cols.first == cols.second);
    assert(cols.second >= 0 and (idx_t) cols.second <= ncols(A));
    assert(cols.first <= cols.second);
    return LegacyMatrix<T, idx_t, layout>(A.m, cols.second - cols.first,
                                          (layout == Layout::ColMajor)
                                              ? &A.ptr[cols.first * A.ldim]
                                              : &A.ptr[cols.first],
                                          A.ldim);
}
 
// Get a column of a column-major LegacyMatrix
template <typename T, class idx_t>
constexpr auto col(LegacyMatrix<T, idx_t>& A,
                   size_type<LegacyMatrix<T, idx_t>> colIdx) noexcept
{
    assert(colIdx >= 0 and colIdx < ncols(A));
    return LegacyVector<T, idx_t>(A.m, &A.ptr[colIdx * A.ldim]);
}
 
// Get a column of a row-major LegacyMatrix
template <typename T, class idx_t>
constexpr auto col(
    LegacyMatrix<T, idx_t, Layout::RowMajor>& A,
    size_type<LegacyMatrix<T, idx_t, Layout::RowMajor>> colIdx) noexcept
{
    assert(colIdx >= 0 and colIdx < ncols(A));
    return LegacyVector<T, idx_t, idx_t>(A.m, &A.ptr[colIdx], A.ldim);
}
 
// Diagonal of a LegacyMatrix
template <typename T, class idx_t, Layout layout>
constexpr auto diag(LegacyMatrix<T, idx_t, layout>& A, int diagIdx = 0) noexcept
{
    assert(diagIdx >= 0 || (idx_t)(-diagIdx) < nrows(A));
    assert(diagIdx <= 0 || (idx_t)diagIdx < ncols(A));
    T* ptr =
        (layout == Layout::ColMajor)
            ? ((diagIdx >= 0) ? &A.ptr[diagIdx * A.ldim] : &A.ptr[-diagIdx])
            : ((diagIdx >= 0) ? &A.ptr[diagIdx] : &A.ptr[-diagIdx * A.ldim]);
    idx_t n = (diagIdx >= 0) ? std::min(A.m + diagIdx, A.n) - (idx_t)diagIdx
                             : std::min(A.m, A.n - diagIdx) + (idx_t)diagIdx;
 
    return LegacyVector<T, idx_t, idx_t>(n, ptr, A.ldim + 1);
}
 
// Transpose view of a LegacyMatrix
template <typename T, class idx_t>
constexpr auto transpose_view(
    LegacyMatrix<T, idx_t, Layout::ColMajor>& A) noexcept
{
    return LegacyMatrix<T, idx_t, Layout::RowMajor>(A.n, A.m, A.ptr, A.ldim);
}
template <typename T, class idx_t>
constexpr auto transpose_view(
    LegacyMatrix<T, idx_t, Layout::RowMajor>& A) noexcept
{
    return LegacyMatrix<T, idx_t, Layout::ColMajor>(A.n, A.m, A.ptr, A.ldim);
}
 
// slice LegacyVector
template <typename T,
          class idx_t,
          typename int_t,
          Direction direction,
          class SliceSpec>
constexpr auto slice(LegacyVector<T, idx_t, int_t, direction>& v,
                     SliceSpec&& rows) noexcept
{
    assert((rows.first >= 0 and (idx_t) rows.first < size(v)) ||
           rows.first == rows.second);
    assert(rows.second >= 0 and (idx_t) rows.second <= size(v));
    assert(rows.first <= rows.second);
    return LegacyVector<T, idx_t, int_t, direction>(
        rows.second - rows.first, &v.ptr[rows.first * v.inc], v.inc);
}
 
// Reshape LegacyMatrix
template <typename T, class idx_t, Layout layout>
auto reshape(LegacyMatrix<T, idx_t, layout>& A,
             size_type<LegacyMatrix<T, idx_t>> m,
             size_type<LegacyMatrix<T, idx_t>> n)
{
    using matrix_t = LegacyMatrix<T, idx_t, layout>;
 
    // constants
    const idx_t size = A.m * A.n;
    const idx_t new_size = m * n;
    const bool is_contiguous =
        (size <= 1) ||
        (layout == Layout::ColMajor && (A.ldim == A.m || A.n <= 1)) ||
        (layout == Layout::RowMajor && (A.ldim == A.n || A.m <= 1));
 
    // Check arguments
    if (new_size > size)
        throw std::domain_error("New size is larger than current size");
 
    if (is_contiguous) {
        return std::make_pair(
            matrix_t(m, n, &A.ptr[0]),
            (layout == Layout::ColMajor)
                ? matrix_t(size - new_size, 1, &A.ptr[0] + new_size)
                : matrix_t(1, size - new_size, &A.ptr[0] + new_size));
    }
    else {
        if (m == A.m || n == 0)
            return std::make_pair(cols(A, std::pair{(idx_t)0, n}),
                                  cols(A, std::pair{n, A.n}));
        else if (n == A.n || m == 0)
            return std::make_pair(rows(A, std::pair{(idx_t)0, m}),
                                  rows(A, std::pair{m, A.m}));
        else
            throw std::domain_error(
                "Cannot reshape to non-contiguous matrix into a matrix if both "
                "the number of rows and columns are different from the new "
                "ones.");
    }
}
template <typename T, class idx_t, Layout layout>
auto reshape(LegacyMatrix<T, idx_t, layout>& A,
             size_type<LegacyMatrix<T, idx_t>> n)
{
    using vector_t = LegacyVector<T, idx_t, idx_t>;
    using matrix_t = LegacyMatrix<T, idx_t, layout>;
 
    // constants
    const idx_t size = A.m * A.n;
    const bool is_contiguous =
        (size <= 1) ||
        (layout == Layout::ColMajor && (A.ldim == A.m || A.n <= 1)) ||
        (layout == Layout::RowMajor && (A.ldim == A.n || A.m <= 1));
 
    // Check arguments
    if (n > size)
        throw std::domain_error("New size is larger than current size");
 
    if (is_contiguous) {
        return std::make_pair(vector_t(n, &A.ptr[0]),
                              (layout == Layout::ColMajor)
                                  ? matrix_t(size - n, 1, &A.ptr[0] + n)
                                  : matrix_t(1, size - n, &A.ptr[0] + n));
    }
    else {
        if (n == 0) {
            return std::make_pair(vector_t(0, &A.ptr[0]), A);
        }
        else if (n == A.m) {
            if constexpr (layout == Layout::ColMajor)
                return std::make_pair(
                    vector_t(n, &A.ptr[0], 1),
                    matrix_t(A.m, A.n - 1, &A.ptr[0] + A.ldim, A.ldim));
            else
                return std::make_pair(
                    vector_t(n, &A.ptr[0], A.ldim),
                    matrix_t(A.m, A.n - 1, &A.ptr[0] + 1, A.ldim));
        }
        else if (n == A.n) {
            if constexpr (layout == Layout::ColMajor)
                return std::make_pair(
                    vector_t(n, &A.ptr[0], A.ldim),
                    matrix_t(A.m - 1, A.n, &A.ptr[0] + 1, A.ldim));
            else
                return std::make_pair(
                    vector_t(n, &A.ptr[0], 1),
                    matrix_t(A.m - 1, A.n, &A.ptr[0] + A.ldim, A.ldim));
        }
        else {
            throw std::domain_error(
                "Cannot reshape to non-contiguous matrix into a vector if the "
                "new size is different from the number of rows and columns.");
        }
    }
}
 
// Reshape LegacyVector
template <typename T, class idx_t, typename int_t, Direction direction>
auto reshape(LegacyVector<T, idx_t, int_t, direction>& v,
             size_type<LegacyMatrix<T, idx_t>> m,
             size_type<LegacyMatrix<T, idx_t>> n)
{
    using matrix_t = LegacyMatrix<T, idx_t, Layout::ColMajor>;
    using vector_t = LegacyVector<T, idx_t, int_t, direction>;
 
    // constants
    const idx_t new_size = m * n;
    const idx_t s = v.n - new_size;
    const bool is_contiguous = (v.inc == 1) || (v.n <= 1);
 
    // Check arguments
    if (new_size > v.n)
        throw std::domain_error("New size is larger than current size");
    if (!is_contiguous && m > 1)
        throw std::domain_error(
            "New sizes are not compatible with the current vector.");
 
    if (is_contiguous) {
        return std::make_pair(matrix_t(m, n, &v.ptr[0]),
                              vector_t(s, &v.ptr[0] + new_size));
    }
    else {
        return std::make_pair(matrix_t(m, n, &v.ptr[0], v.inc),
                              vector_t(s, &v.ptr[0] + new_size * v.inc, v.inc));
    }
}
template <typename T, class idx_t, typename int_t, Direction direction>
auto reshape(LegacyVector<T, idx_t, int_t, direction>& v,
             size_type<LegacyMatrix<T, idx_t>> n)
{
    // Check arguments
    if (n > v.n)
        throw std::domain_error("New size is larger than current size");
 
    return std::make_pair(slice(v, std::pair{(idx_t)0, n}),
                          slice(v, std::pair{n, v.n}));
}
 
// -----------------------------------------------------------------------------
// Deduce matrix and vector type from two provided ones
 
namespace traits {
 
    template <typename T>
    constexpr bool cast_to_legacy_type =
        is_legacy_type<T> || is_stdvector_type<T>
#ifdef TLAPACK_EIGEN_HH
        || is_eigen_type<T>
#endif
#ifdef TLAPACK_MDSPAN_HH
        || is_mdspan_type<T>
#endif
        ;
 
    // for two types
    // should be especialized for every new matrix class
    template <class matrixA_t, typename matrixB_t>
    struct matrix_type_traits<
        matrixA_t,
        matrixB_t,
        typename std::enable_if<
            ((is_legacy_type<matrixA_t> ||
              is_legacy_type<matrixB_t>)&&cast_to_legacy_type<matrixA_t> &&
             cast_to_legacy_type<matrixB_t>),
            int>::type> {
        using T = scalar_type<type_t<matrixA_t>, type_t<matrixB_t>>;
        using idx_t = size_type<matrixA_t>;
 
        static constexpr Layout LA = layout<matrixA_t>;
        static constexpr Layout LB = layout<matrixB_t>;
        static constexpr Layout L =
            ((LA == Layout::RowMajor) && (LB == Layout::RowMajor))
                ? Layout::RowMajor
                : Layout::ColMajor;
 
        using type = LegacyMatrix<T, idx_t, L>;
    };
 
    // for two types
    // should be especialized for every new vector class
    template <typename vecA_t, typename vecB_t>
    struct vector_type_traits<
        vecA_t,
        vecB_t,
        typename std::enable_if<
            ((is_legacy_type<vecA_t> ||
              is_legacy_type<vecB_t>)&&cast_to_legacy_type<vecA_t> &&
             cast_to_legacy_type<vecB_t>),
            int>::type> {
        using T = scalar_type<type_t<vecA_t>, type_t<vecB_t>>;
        using idx_t = size_type<vecA_t>;
 
        using type = LegacyVector<T, idx_t, idx_t>;
    };
 
#if !defined(TLAPACK_EIGEN_HH) && !defined(TLAPACK_MDSPAN_HH)
    template <class vecA_t, class vecB_t>
    struct matrix_type_traits<
        vecA_t,
        vecB_t,
        std::enable_if_t<traits::is_stdvector_type<vecA_t> &&
                             traits::is_stdvector_type<vecB_t>,
                         int>> {
        using T = scalar_type<type_t<vecA_t>, type_t<vecB_t>>;
        using type = LegacyMatrix<T>;
    };
 
    template <class vecA_t, class vecB_t>
    struct vector_type_traits<
        vecA_t,
        vecB_t,
        std::enable_if_t<traits::is_stdvector_type<vecA_t> &&
                             traits::is_stdvector_type<vecB_t>,
                         int>> {
        using T = scalar_type<type_t<vecA_t>, type_t<vecB_t>>;
        using type = LegacyVector<T>;
    };
#endif
 
}  // namespace traits
 
// -----------------------------------------------------------------------------
// Cast to Legacy arrays
 
template <typename T, class idx_t, Layout layout>
constexpr auto legacy_matrix(const LegacyMatrix<T, idx_t, layout>& A) noexcept
{
    return legacy::Matrix<T, idx_t>{layout, A.m, A.n, A.ptr, A.ldim};
}
 
template <class T, class idx_t, class int_t, Direction direction>
constexpr auto legacy_matrix(
    const LegacyVector<T, idx_t, int_t, direction>& v) noexcept
{
    return legacy::Matrix<T, idx_t>{Layout::ColMajor, 1, v.n, v.ptr,
                                    (idx_t)v.inc};
}
 
template <typename T, class idx_t, typename int_t, Direction direction>
constexpr auto legacy_vector(
    const LegacyVector<T, idx_t, int_t, direction>& v) noexcept
{
    assert(direction == Direction::Forward || std::is_signed<idx_t>::value ||
           v.inc == 0);
 
    return legacy::Vector<T, idx_t>{
        v.n, v.ptr,
        (direction == Direction::Forward) ? idx_t(v.inc) : idx_t(-v.inc)};
}
 
}  // namespace tlapack
 
#endif  // TLAPACK_LEGACYARRAY_HH