Tpetra_Details_extractBlockDiagonal.hpp

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// @HEADER
// *****************************************************************************
//          Tpetra: Templated Linear Algebra Services Package
//
// Copyright 2008 NTESS and the Tpetra contributors.
// SPDX-License-Identifier: BSD-3-Clause
// *****************************************************************************
// @HEADER
 
#ifndef TPETRA_DETAILS_EXTRACTBLOCKDIAGONAL_HPP
#define TPETRA_DETAILS_EXTRACTBLOCKDIAGONAL_HPP
 
#include "TpetraCore_config.h"
#include "Tpetra_CrsMatrix.hpp"
#include "Teuchos_RCP.hpp"
#include "Tpetra_Details_Behavior.hpp"
 
 
namespace Tpetra {
namespace Details {
 
template <class SparseMatrixType,
          class MultiVectorType>
void extractBlockDiagonal(const SparseMatrixType& A, MultiVectorType& diagonal) {
  using local_map_type = typename SparseMatrixType::map_type::local_map_type;
  using SC             = typename MultiVectorType::scalar_type;
  using LO             = typename SparseMatrixType::local_ordinal_type;
  using KCRS           = typename SparseMatrixType::local_matrix_device_type;
  using lno_view_t     = typename KCRS::StaticCrsGraphType::row_map_type::const_type;
  using lno_nnz_view_t = typename KCRS::StaticCrsGraphType::entries_type::const_type;
  using scalar_view_t  = typename KCRS::values_type::const_type;
  using local_mv_type  = typename MultiVectorType::dual_view_type::t_dev;
  using range_type     = Kokkos::RangePolicy<typename SparseMatrixType::node_type::execution_space, LO>;
#if KOKKOS_VERSION >= 40799
  using ATS = KokkosKernels::ArithTraits<SC>;
#else
  using ATS      = Kokkos::ArithTraits<SC>;
#endif
#if KOKKOS_VERSION >= 40799
  using impl_ATS = KokkosKernels::ArithTraits<typename ATS::val_type>;
#else
  using impl_ATS = Kokkos::ArithTraits<typename ATS::val_type>;
#endif
 
  // Sanity checking: Map Compatibility (A's rowmap matches diagonal's map)
  if (Tpetra::Details::Behavior::debug() == true) {
    TEUCHOS_TEST_FOR_EXCEPTION(!A.getRowMap()->isSameAs(*diagonal.getMap()),
                               std::runtime_error, "Tpetra::Details::extractBlockDiagonal was given incompatible maps");
  }
 
  LO numrows   = diagonal.getLocalLength();
  LO blocksize = diagonal.getNumVectors();
 
  // Get Kokkos versions of objects
  local_map_type rowmap  = A.getRowMap()->getLocalMap();
  local_map_type colmap  = A.getRowMap()->getLocalMap();
  local_mv_type diag     = diagonal.getLocalViewDevice(Access::OverwriteAll);
  const KCRS Amat        = A.getLocalMatrixDevice();
  lno_view_t Arowptr     = Amat.graph.row_map;
  lno_nnz_view_t Acolind = Amat.graph.entries;
  scalar_view_t Avals    = Amat.values;
 
  Kokkos::parallel_for(
      "Tpetra::extractBlockDiagonal", range_type(0, numrows), KOKKOS_LAMBDA(const LO i) {
        LO diag_col   = colmap.getLocalElement(rowmap.getGlobalElement(i));
        LO blockStart = diag_col - (diag_col % blocksize);
        LO blockStop  = blockStart + blocksize;
        for (LO k = 0; k < blocksize; k++)
          diag(i, k) = impl_ATS::zero();
 
        for (size_t k = Arowptr(i); k < Arowptr(i + 1); k++) {
          LO col = Acolind(k);
          if (blockStart <= col && col < blockStop) {
            diag(i, col - blockStart) = Avals(k);
          }
        }
      });
}
 
}  // namespace Details
}  // namespace Tpetra
 
#endif  // TPETRA_DETAILS_EXTRACTBLOCKDIAGONAL_HPP