infnorm_colmajor.hpp

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//
// Copyright (c) 2021-2023, 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_COLMAJOR_HH
#define TLAPACK_INFNORM_COLMAJOR_HH
 
#include "tlapack/base/utils.hpp"
 
namespace tlapack {
 
template <class T, TLAPACK_MATRIX matrix_t>
constexpr WorkInfo infnorm_colmajor_worksize(const matrix_t& A)
{
    return WorkInfo(nrows(A));
}
 
template <TLAPACK_MATRIX matrix_t, TLAPACK_WORKSPACE work_t>
auto infnorm_colmajor_work(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>;
 
    // constants
    const idx_t m = nrows(A);
    const idx_t n = ncols(A);
 
    // quick return
    if (m == 0 || n == 0) return real_t(0);
 
    // Vector w
    auto [w, work1] = reshape(work, m);
 
    // Norm value
    real_t norm(0);
 
    for (idx_t i = 0; i < m; ++i)
        w[i] = abs(A(i, 0));
 
    for (idx_t j = 1; j < n; ++j)
        for (idx_t i = 0; i < m; ++i)
            w[i] += abs(A(i, j));
 
    for (idx_t i = 0; i < m; ++i) {
        real_t temp = w[i];
 
        if (temp > norm)
            norm = temp;
        else {
            if (isnan(temp)) return temp;
        }
    }
 
    return norm;
}
 
template <TLAPACK_MATRIX matrix_t>
auto infnorm_colmajor(const matrix_t& A)
{
    using T = type_t<matrix_t>;
    using real_t = real_type<T>;
    using idx_t = size_type<matrix_t>;
 
    // constants
    const idx_t m = nrows(A);
    const idx_t n = ncols(A);
 
    // quick return
    if (m == 0 || n == 0) return real_t(0);
 
    // Allocates workspace
    WorkInfo workinfo = infnorm_colmajor_worksize<T>(A);
    std::vector<T> work_;
    auto work = new_matrix(work_, workinfo.m, workinfo.n);
 
    return infnorm_colmajor_work(A, work);
}
 
}  // namespace tlapack
 
#endif  // TLAPACK_INFNORM_COLMAJOR_HH