diagonal_preconditioner.h

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//
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// Copyright (C) 2022 - 2026 by the ryujin authors
//
 
#pragma once
 
#include <compile_time_options.h>
 
#include "state_vector.h"
 
#include <deal.II/lac/la_parallel_block_vector.h>
 
namespace ryujin
{
  template <typename Number>
  class DiagonalPreconditioner
  {
  public:
    using ScalarHostVector = typename Vectors::ScalarHostVector<Number>;
 
    using BlockHostVector = typename Vectors::BlockHostVector<Number>;
 
    DiagonalPreconditioner() = default;
 
    void reinit(const std::shared_ptr<const dealii::Utilities::MPI::Partitioner>
                    &scalar_partitioner)
    {
      diagonal_.reinit(scalar_partitioner);
    }
 
    ScalarHostVector &scaling_vector()
    {
      return diagonal_;
    }
 
    void vmult(ScalarHostVector &dst, const ScalarHostVector &src) const
    {
      const auto n_owned = diagonal_.get_partitioner()->locally_owned_size();
      AssertDimension(n_owned, src.get_partitioner()->locally_owned_size());
      AssertDimension(n_owned, dst.get_partitioner()->locally_owned_size());
 
      DEAL_II_OPENMP_SIMD_PRAGMA
      for (unsigned int i = 0; i < n_owned; ++i)
        dst.local_element(i) =
            diagonal_.local_element(i) * src.local_element(i);
    }
 
    void vmult(BlockHostVector &dst, const BlockHostVector &src) const
    {
      const auto n_blocks = src.n_blocks();
      AssertDimension(n_blocks, dst.n_blocks());
 
      const auto n_owned = diagonal_.get_partitioner()->locally_owned_size();
 
      for (unsigned int d = 0; d < n_blocks; ++d) {
        AssertDimension(n_owned,
                        src.block(d).get_partitioner()->locally_owned_size());
        AssertDimension(n_owned,
                        dst.block(d).get_partitioner()->locally_owned_size());
 
        DEAL_II_OPENMP_SIMD_PRAGMA
        for (unsigned int i = 0; i < n_owned; ++i)
          dst.block(d).local_element(i) =
              diagonal_.local_element(i) * src.block(d).local_element(i);
      }
    }
 
  private:
    ScalarHostVector diagonal_;
  };
 
} /* namespace ryujin */