gelss.hpp

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// Copyright (c) 2020-2024 Simons Foundation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0.txt
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Authors: Thomas Hahn, Jason Kaye, Olivier Parcollet, Nils Wentzell
 
#pragma once
 
#include "./interface/cxx_interface.hpp"
#include "../basic_array.hpp"
#include "../concepts.hpp"
#include "../declarations.hpp"
#include "../exceptions.hpp"
#include "../macros.hpp"
#include "../mem/address_space.hpp"
#include "../traits.hpp"
 
#include <algorithm>
#include <cmath>
#include <complex>
 
namespace nda::lapack {
 
  template <MemoryMatrix A, MemoryArray B, MemoryVector S>
    requires(have_same_value_type_v<A, B> and mem::on_host<A, B, S> and is_blas_lapack_v<get_value_t<A>>)
  int gelss(A &&a, B &&b, S &&s, double rcond, int &rank) { // NOLINT (temporary views are allowed here)
    static_assert(has_F_layout<A> and has_F_layout<B>, "Error in nda::lapack::gelss: C order not supported");
    static_assert(MemoryVector<B> or MemoryMatrix<B>, "Error in nda::lapack::gelss: B must be a vector or a matrix");
 
    auto dm = std::min(a.extent(0), a.extent(1));
    if (s.size() < dm) s.resize(dm);
 
    // must be lapack compatible
    EXPECTS(a.indexmap().min_stride() == 1);
    EXPECTS(b.indexmap().min_stride() == 1);
    EXPECTS(s.indexmap().min_stride() == 1);
 
    // first call to get the optimal bufferSize
    using value_type = get_value_t<A>;
    value_type bufferSize_T{};
    auto rwork = array<double, 1>(5 * dm);
    int info   = 0;
    int nrhs = 1, ldb = b.size(); // defaults for B MemoryVector
    if constexpr (MemoryMatrix<B>) {
      nrhs = b.extent(1);
      ldb  = get_ld(b);
    }
    f77::gelss(a.extent(0), a.extent(1), nrhs, a.data(), get_ld(a), b.data(), ldb, s.data(), rcond, rank, &bufferSize_T, -1, rwork.data(), info);
    int bufferSize = static_cast<int>(std::ceil(std::real(bufferSize_T)));
 
    // allocate work buffer and perform actual library call
    array<value_type, 1> work(bufferSize);
    f77::gelss(a.extent(0), a.extent(1), nrhs, a.data(), get_ld(a), b.data(), ldb, s.data(), rcond, rank, work.data(), bufferSize, rwork.data(),
               info);
 
    if (info) NDA_RUNTIME_ERROR << "Error in nda::lapack::gelss: info = " << info;
    return info;
  }
 
} // namespace nda::lapack