blas1_matrix_frob_norm.hpp

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// SPDX-License-Identifier: BSL-1.0
// SPDX-FileCopyrightText: Copyright (C) 2023 Tobias Hienzsch
 
#ifndef TETL_LINALG_BLAS1_MATRIX_FROB_NORM_HPP
#define TETL_LINALG_BLAS1_MATRIX_FROB_NORM_HPP
 
#include <etl/_cmath/sqrt.hpp>
#include <etl/_linalg/concepts.hpp>
#include <etl/_type_traits/declval.hpp>
#include <etl/_utility/cmp_less.hpp>
 
namespace etl::linalg {
 
/// \ingroup linalg
template <in_matrix InMat, typename Scalar>
[[nodiscard]] constexpr auto matrix_frob_norm(InMat a, Scalar init) -> Scalar
{
    auto result = init;
    for (typename InMat::size_type row{0}; etl::cmp_less(row, a.extent(0)); ++row) {
        for (typename InMat::size_type col{0}; etl::cmp_less(col, a.extent(1)); ++col) {
            result += detail::abs_if_needed(a(row, col));
        }
    }
 
    using etl::sqrt;
    return static_cast<Scalar>(sqrt(result));
}
 
/// \ingroup linalg
template <in_matrix InMat>
[[nodiscard]] constexpr auto matrix_frob_norm(InMat a)
{
    using abs_type    = decltype(detail::abs_if_needed(declval<typename InMat::value_type>()));
    using return_type = decltype(declval<abs_type>() * declval<abs_type>());
    return matrix_frob_norm(a, return_type{});
}
 
} // namespace etl::linalg
 
#endif // TETL_LINALG_BLAS1_MATRIX_FROB_NORM_HPP