infnorm_hermitian_colmajor.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_INFNORM_HE_COLMAJOR_HH
#define TLAPACK_INFNORM_HE_COLMAJOR_HH
 
#include "tlapack/base/utils.hpp"
 
namespace tlapack {
 
template <class T, TLAPACK_UPLO uplo_t, TLAPACK_MATRIX matrix_t>
constexpr WorkInfo infnorm_hermitian_colmajor_worksize(uplo_t uplo,
                                                       const matrix_t& A)
{
    return WorkInfo(nrows(A));
}
 
template <TLAPACK_UPLO uplo_t,
          TLAPACK_MATRIX matrix_t,
          TLAPACK_WORKSPACE work_t>
auto infnorm_hermitian_colmajor_work(uplo_t uplo,
                                     const matrix_t& A,
                                     work_t& work)
{
    using T = type_t<matrix_t>;
    using real_t = real_type<T>;
    using idx_t = size_type<matrix_t>;
    using range = pair<idx_t, idx_t>;
 
    // check arguments
    tlapack_check_false(uplo != Uplo::Lower && uplo != Uplo::Upper);
 
    // constants
    const idx_t n = nrows(A);
 
    // quick return
    if (n <= 0) return real_t(0);
 
    // Vector w
    auto [w, work1] = reshape(work, n);
 
    // Norm value
    real_t norm(0);
 
    for (idx_t i = 0; i < n; ++i)
        w[i] = T(0);
 
    if (uplo == Uplo::Upper) {
        for (idx_t j = 0; j < n; ++j) {
            real_t sum(0);
            for (idx_t i = 0; i < j; ++i) {
                const real_t absa = abs(A(i, j));
                sum += absa;
                w[i] += absa;
            }
            w[j] = sum + abs(real(A(j, j)));
        }
        for (idx_t i = 0; i < n; ++i) {
            real_t sum = w[i];
            if (sum > norm)
                norm = sum;
            else {
                if (isnan(sum)) return sum;
            }
        }
    }
    else {
        for (idx_t j = 0; j < n; ++j) {
            real_t sum = w[j] + abs(real(A(j, j)));
            for (idx_t i = j + 1; i < n; ++i) {
                const real_t absa = abs(A(i, j));
                sum += absa;
                w[i] += absa;
            }
            if (sum > norm)
                norm = sum;
            else {
                if (isnan(sum)) return sum;
            }
        }
    }
 
    return norm;
}
 
template <TLAPACK_UPLO uplo_t, TLAPACK_MATRIX matrix_t>
auto infnorm_hermitian_colmajor(uplo_t uplo, const matrix_t& A)
{
    using T = type_t<matrix_t>;
    using real_t = real_type<T>;
    using idx_t = size_type<matrix_t>;
 
    // check arguments
    tlapack_check_false(uplo != Uplo::Lower && uplo != Uplo::Upper);
 
    // constants
    const idx_t n = nrows(A);
 
    // quick return
    if (n <= 0) return real_t(0);
 
    // Allocates workspace
    WorkInfo workinfo = infnorm_hermitian_colmajor_worksize<T>(uplo, A);
    std::vector<T> work_;
    auto work = new_matrix(work_, workinfo.m, workinfo.n);
 
    return infnorm_hermitian_colmajor_work(uplo, A, work);
}
 
}  // namespace tlapack
 
#endif  // TLAPACK_INFNORM_HE_COLMAJOR_HH