geqp3.hpp

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// Copyright (c) 2024--present, The Simons Foundation
// This file is part of TRIQS/nda and is licensed under the Apache License, Version 2.0.
// SPDX-License-Identifier: Apache-2.0
// See LICENSE in the root of this distribution for details.

 
#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>
#include <type_traits>
 
namespace nda::lapack {

  template <MemoryMatrix A, MemoryVector JPVT, MemoryVector TAU>
    requires(mem::on_host<A> and is_blas_lapack_v<get_value_t<A>> and have_same_value_type_v<A, TAU>
             and mem::have_compatible_addr_space<A, JPVT, TAU>)
  int geqp3(A &&a, JPVT &&jpvt, TAU &&tau) { // NOLINT (temporary views are allowed here)
    static_assert(has_F_layout<A>, "Error in nda::lapack::geqp3: C order not supported");
    static_assert(std::is_same_v<get_value_t<JPVT>, int>, "Error in nda::lapack::geqp3: Pivoting array must have elements of type int");
    static_assert(mem::have_host_compatible_addr_space<A, JPVT, TAU>, "Error in nda::lapack::geqp3: Only CPU is supported");
 
    auto [m, n] = a.shape();
    EXPECTS(tau.size() >= std::min(m, n));
 
    // must be lapack compatible
    EXPECTS(a.indexmap().min_stride() == 1);
    EXPECTS(jpvt.indexmap().min_stride() == 1);
    EXPECTS(tau.indexmap().min_stride() == 1);
 
    // first call to get the optimal buffersize
    using value_type = get_value_t<A>;
    value_type bufferSize_T{};
    int info = 0;
    array<double, 1> rwork(2 * n);
    lapack::f77::geqp3(m, n, a.data(), get_ld(a), jpvt.data(), tau.data(), &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
    nda::array<value_type, 1> work(bufferSize);
    lapack::f77::geqp3(m, n, a.data(), get_ld(a), jpvt.data(), tau.data(), work.data(), bufferSize, rwork.data(), info);
    jpvt -= 1; // Shift to 0-based indexing
 
    if (info) NDA_RUNTIME_ERROR << "Error in nda::lapack::geqp3: info = " << info;
    return info;
  }
 
} // namespace nda::lapack