qr_iteration.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_QR_ITERATION_HH
#define TLAPACK_QR_ITERATION_HH
 
#include "tlapack/base/utils.hpp"
#include "tlapack/lapack/lahqr.hpp"
#include "tlapack/lapack/multishift_qr.hpp"
 
namespace tlapack {
 
enum class QRIterationVariant : char { MultiShift = 'M', DoubleShift = 'D' };
 
struct QRIterationOpts : public FrancisOpts {
    QRIterationVariant variant = QRIterationVariant::MultiShift;
};
 
template <class T,
          TLAPACK_MATRIX matrix_t,
          TLAPACK_VECTOR vector_t,
          enable_if_t<is_complex<type_t<vector_t> >, int> = 0>
constexpr WorkInfo qr_iteration_worksize(bool want_t,
                                         bool want_z,
                                         size_type<matrix_t> ilo,
                                         size_type<matrix_t> ihi,
                                         const matrix_t& A,
                                         const vector_t& w,
                                         const matrix_t& Z,
                                         const QRIterationOpts& opts = {})
{
    // Call variant
    if (opts.variant == QRIterationVariant::MultiShift)
        return multishift_qr_worksize<T>(want_t, want_z, ilo, ihi, A, w, Z,
                                         opts);
    else
        return WorkInfo(0);
}
 
template <TLAPACK_MATRIX matrix_t,
          TLAPACK_VECTOR vector_t,
          TLAPACK_WORKSPACE work_t,
          enable_if_t<is_complex<type_t<vector_t> >, int> = 0>
int qr_iteration_work(bool want_t,
                      bool want_z,
                      size_type<matrix_t> ilo,
                      size_type<matrix_t> ihi,
                      matrix_t& A,
                      vector_t& w,
                      matrix_t& Z,
                      work_t& work,
                      QRIterationOpts& opts)
{
    // Call variant
    if (opts.variant == QRIterationVariant::MultiShift)
        return multishift_qr_work(want_t, want_z, ilo, ihi, A, w, Z, work,
                                  opts);
    else
        return lahqr(want_t, want_z, ilo, ihi, A, w, Z);
}
 
template <TLAPACK_MATRIX matrix_t,
          TLAPACK_VECTOR vector_t,
          enable_if_t<is_complex<type_t<vector_t> >, int> = 0>
int qr_iteration(bool want_t,
                 bool want_z,
                 size_type<matrix_t> ilo,
                 size_type<matrix_t> ihi,
                 matrix_t& A,
                 vector_t& w,
                 matrix_t& Z,
                 QRIterationOpts& opts)
{
    // Call variant
    if (opts.variant == QRIterationVariant::MultiShift)
        return multishift_qr(want_t, want_z, ilo, ihi, A, w, Z, opts);
    else
        return lahqr(want_t, want_z, ilo, ihi, A, w, Z);
}
 
}  // namespace tlapack
 
#endif