Ifpack2_Container_def.hpp

// @HEADER
// *****************************************************************************
//       Ifpack2: Templated Object-Oriented Algebraic Preconditioner Package
//
// Copyright 2009 NTESS and the Ifpack2 contributors.
// SPDX-License-Identifier: BSD-3-Clause
// *****************************************************************************
// @HEADER
 
#ifndef IFPACK2_CONTAINER_DEF_HPP
#define IFPACK2_CONTAINER_DEF_HPP
 
#include <Ifpack2_Details_MultiVectorLocalGatherScatter.hpp>
#include "Ifpack2_Details_Behavior.hpp"
#include <Teuchos_Time.hpp>
 
namespace Ifpack2 {
 
// Implementation of Ifpack2::Container
 
template <class MatrixType>
Container<MatrixType>::Container(
    const Teuchos::RCP<const row_matrix_type>& matrix,
    const Teuchos::Array<Teuchos::Array<LO>>& partitions,
    bool pointIndexed)
  : inputMatrix_(matrix)
  , inputCrsMatrix_(Teuchos::rcp_dynamic_cast<const crs_matrix_type>(inputMatrix_))
  , inputBlockMatrix_(Teuchos::rcp_dynamic_cast<const block_crs_matrix_type>(inputMatrix_))
  , pointIndexed_(pointIndexed)
  , IsInitialized_(false)
  , IsComputed_(false) {
  using Teuchos::Array;
  using Teuchos::ArrayView;
  using Teuchos::Comm;
  using Teuchos::Ptr;
  using Teuchos::RCP;
  NumLocalRows_      = inputMatrix_->getLocalNumRows();
  NumGlobalRows_     = inputMatrix_->getGlobalNumRows();
  NumGlobalNonzeros_ = inputMatrix_->getGlobalNumEntries();
  IsParallel_        = inputMatrix_->getRowMap()->getComm()->getSize() != 1;
  hasBlockCrs_       = !inputBlockMatrix_.is_null();
  if (hasBlockCrs_)
    bcrsBlockSize_ = inputBlockMatrix_->getBlockSize();
  else
    bcrsBlockSize_ = 1;
  if (hasBlockCrs_ && !pointIndexed_)
    scalarsPerRow_ = bcrsBlockSize_;
  else
    scalarsPerRow_ = 1;
  setBlockSizes(partitions);
  // Sanity check the partitions
  if (Ifpack2::Details::Behavior::debug()) {
    // Check whether the input set of local row indices is correct.
    const map_type& rowMap = *inputMatrix_->getRowMap();
    for (int i = 0; i < numBlocks_; i++) {
      Teuchos::ArrayView<const LO> blockRows = getBlockRows(i);
      for (LO j = 0; j < blockSizes_[i]; j++) {
        LO row = blockRows[j];
        if (pointIndexed) {
          // convert the point row to the corresponding block row
          row /= bcrsBlockSize_;
        }
        TEUCHOS_TEST_FOR_EXCEPTION(
            !rowMap.isNodeLocalElement(row),
            std::invalid_argument,
            "Ifpack2::Container: "
            "On process "
                << rowMap.getComm()->getRank() << " of "
                << rowMap.getComm()->getSize() << ", in the given set of local row "
                                                  "indices blockRows = "
                << Teuchos::toString(blockRows) << ", the following "
                                                   "entries is not valid local row index on the calling process: "
                << row << ".");
      }
    }
  }
}
 
template <class MatrixType>
Container<MatrixType>::
    ~Container() {}
 
template <class MatrixType>
Teuchos::ArrayView<const typename MatrixType::local_ordinal_type>
Container<MatrixType>::getBlockRows(int blockIndex) const {
  return Teuchos::ArrayView<const LO>(&blockRows_[blockOffsets_[blockIndex]], blockSizes_[blockIndex]);
}
 
template <class MatrixType>
void Container<MatrixType>::setBlockSizes(const Teuchos::Array<Teuchos::Array<LO>>& partitions) {
  // First, create a grand total of all the rows in all the blocks
  // Note: If partitioner allowed overlap, this could be greater than the # of local rows
  LO totalBlockRows = 0;
  numBlocks_        = partitions.size();
  blockSizes_.resize(numBlocks_);
  blockOffsets_.resize(numBlocks_);
  maxBlockSize_ = 0;
  for (int i = 0; i < numBlocks_; i++) {
    LO rowsInBlock   = partitions[i].size();
    blockSizes_[i]   = rowsInBlock;
    blockOffsets_[i] = totalBlockRows;
    totalBlockRows += rowsInBlock;
    maxBlockSize_ = std::max(maxBlockSize_, rowsInBlock * scalarsPerRow_);
  }
  blockRows_.resize(totalBlockRows);
  // set blockRows_: each entry is the partition/block of the row
  LO iter = 0;
  for (int i = 0; i < numBlocks_; i++) {
    for (int j = 0; j < blockSizes_[i]; j++) {
      blockRows_[iter++] = partitions[i][j];
    }
  }
}
 
template <class MatrixType>
void Container<MatrixType>::getMatDiag() const {
  if (Diag_.is_null()) {
    Diag_ = rcp(new vector_type(inputMatrix_->getDomainMap()));
    inputMatrix_->getLocalDiagCopy(*Diag_);
  }
}
 
template <class MatrixType>
bool Container<MatrixType>::isInitialized() const {
  return IsInitialized_;
}
 
template <class MatrixType>
bool Container<MatrixType>::isComputed() const {
  return IsComputed_;
}
 
template <class MatrixType>
void Container<MatrixType>::
    applyMV(const mv_type& /*X*/, mv_type& /*Y*/) const {
  TEUCHOS_TEST_FOR_EXCEPT_MSG(true, "Not implemented.");
}
 
template <class MatrixType>
void Container<MatrixType>::
    weightedApplyMV(const mv_type& /*X*/, mv_type& /*Y*/, vector_type& /*W*/) const {
  TEUCHOS_TEST_FOR_EXCEPT_MSG(true, "Not implemented.");
}
 
template <class MatrixType>
std::string Container<MatrixType>::
    getName() {
  return "Generic";
}
 
template <class MatrixType>
void Container<MatrixType>::DoGSBlock(ConstHostView /*X*/, HostView /*Y*/, HostView /*Y2*/, HostView /*Resid*/,
                                      SC /*dampingFactor*/, LO /*i*/) const {
  TEUCHOS_TEST_FOR_EXCEPT_MSG(true, "Not implemented.");
}
 
template <class MatrixType>
void Container<MatrixType>::DoJacobi(ConstHostView X, HostView Y, SC dampingFactor) const {
  using STS     = Teuchos::ScalarTraits<ISC>;
  const ISC one = STS::one();
  // use blockRows_ and blockSizes_
  size_t numVecs = X.extent(1);
  // Non-overlapping Jacobi
  for (LO i = 0; i < numBlocks_; i++) {
    // may happen that a partition is empty
    if (blockSizes_[i] != 1 || hasBlockCrs_) {
      if (blockSizes_[i] == 0)
        continue;
      apply(X, Y, i, Teuchos::NO_TRANS, dampingFactor, one);
    } else  // singleton, can't access Containers_[i] as it was never filled and may be null.
    {
      LO LRID = blockRows_[blockOffsets_[i]];
      getMatDiag();
      auto diagView = Diag_->getLocalViewHost(Tpetra::Access::ReadOnly);
      ISC d         = one * (static_cast<ISC>(dampingFactor)) / diagView(LRID, 0);
      for (size_t nv = 0; nv < numVecs; nv++) {
        ISC x = X(LRID, nv);
        Y(LRID, nv) += x * d;
      }
    }
  }
}
 
template <class MatrixType>
void Container<MatrixType>::DoOverlappingJacobi(ConstHostView X, HostView Y, ConstHostView W, SC dampingFactor, bool nonsymScaling) const {
  using STS = Teuchos::ScalarTraits<SC>;
  // Overlapping Jacobi
  for (LO i = 0; i < numBlocks_; i++) {
    // may happen that a partition is empty
    if (blockSizes_[i] == 0)
      continue;
    if (blockSizes_[i] != 1) {
      if (!nonsymScaling)
        weightedApply(X, Y, W, i, Teuchos::NO_TRANS, dampingFactor, STS::one());
      else {
        // A crummy way of doing nonsymmetric scaling. We effectively
        // first reverse scale x, which later gets scaled inside weightedApply
        // so the net effect is that x is not scaled.
        // This was done to keep using weightedApply() that is defined in
        // many spots in the code.
        HostView tempo("", X.extent(0), X.extent(1));
        size_t numVecs = X.extent(1);
        LO bOffset     = blockOffsets_[i];
        for (LO ii = 0; ii < blockSizes_[i]; ii++) {
          LO LRID = blockRows_[bOffset++];
          for (size_t jj = 0; jj < numVecs; jj++) tempo(LRID, jj) = X(LRID, jj) / W(LRID, 0);
        }
        weightedApply(tempo, Y, W, i, Teuchos::NO_TRANS, dampingFactor, STS::one());
      }
    } else  // singleton, can't access Containers_[i] as it was never filled and may be null.
    {
      const ISC one  = STS::one();
      size_t numVecs = X.extent(1);
      LO LRID        = blockRows_[blockOffsets_[i]];
      getMatDiag();
      auto diagView = Diag_->getLocalViewHost(Tpetra::Access::ReadOnly);
      ISC recip     = one / diagView(LRID, 0);
      ISC wval      = W(LRID, 0);
      ISC combo     = wval * recip;
      ISC d         = combo * (static_cast<ISC>(dampingFactor));
      for (size_t nv = 0; nv < numVecs; nv++) {
        ISC x       = X(LRID, nv);
        Y(LRID, nv) = x * d + Y(LRID, nv);
      }
    }
  }
}
 
// Do Gauss-Seidel with just block i
// This is used 3 times: once in DoGaussSeidel and twice in DoSGS
template <class MatrixType, typename LocalScalarType>
void ContainerImpl<MatrixType, LocalScalarType>::DoGSBlock(
    ConstHostView X, HostView /*Y*/, HostView Y2, HostView Resid,
    SC dampingFactor, LO i) const {
  using Teuchos::ArrayView;
  using STS      = Teuchos::ScalarTraits<ISC>;
  size_t numVecs = X.extent(1);
  const ISC one  = STS::one();
  if (this->blockSizes_[i] == 0)
    return;  // Skip empty partitions
  if (this->hasBlockCrs_ && !this->pointIndexed_) {
    // Use efficient blocked version
    ArrayView<const LO> blockRows = this->getBlockRows(i);
    const size_t localNumRows     = this->blockSizes_[i];
    using inds_type               = typename block_crs_matrix_type::local_inds_host_view_type;
    using vals_type               = typename block_crs_matrix_type::values_host_view_type;
    for (size_t j = 0; j < localNumRows; j++) {
      LO row = blockRows[j];  // Containers_[i]->ID (j);
      vals_type values;
      inds_type colinds;
      this->inputBlockMatrix_->getLocalRowView(row, colinds, values);
      LO numEntries = (LO)colinds.size();
      for (size_t m = 0; m < numVecs; m++) {
        for (int localR = 0; localR < this->bcrsBlockSize_; localR++)
          Resid(row * this->bcrsBlockSize_ + localR, m) = X(row * this->bcrsBlockSize_ + localR, m);
        for (LO k = 0; k < numEntries; ++k) {
          const LO col = colinds[k];
          for (int localR = 0; localR < this->bcrsBlockSize_; localR++) {
            for (int localC = 0; localC < this->bcrsBlockSize_; localC++) {
              Resid(row * this->bcrsBlockSize_ + localR, m) -=
                  values[k * this->bcrsBlockSize_ * this->bcrsBlockSize_ + localR + localC * this->bcrsBlockSize_] * Y2(col * this->bcrsBlockSize_ + localC, m);
            }
          }
        }
      }
    }
    // solve with this block
    //
    // Note: I'm abusing the ordering information, knowing that X/Y
    // and Y2 have the same ordering for on-proc unknowns.
    //
    // Note: Add flop counts for inverse apply
    apply(Resid, Y2, i, Teuchos::NO_TRANS, dampingFactor, one);
  } else if (!this->hasBlockCrs_ && this->blockSizes_[i] == 1) {
    // singleton, can't access Containers_[i] as it was never filled and may be null.
    // a singleton calculation (just using matrix diagonal) is exact, all residuals should be zero.
    LO LRID = this->blockOffsets_[i];  // by definition, a singleton 1 row in block.
    // Use the KokkosSparse internal matrix for low-overhead values/indices access
    // But, can only do this if the matrix is accessible directly from host, since it's not a DualView
    using container_exec_space = typename ContainerImpl<MatrixType, LocalScalarType>::crs_matrix_type::execution_space;
    container_exec_space().fence();
    auto localA         = this->inputCrsMatrix_->getLocalMatrixHost();
    using size_type     = typename crs_matrix_type::local_matrix_host_type::size_type;
    const auto& rowmap  = localA.graph.row_map;
    const auto& entries = localA.graph.entries;
    const auto& values  = localA.values;
    this->getMatDiag();
    auto diagView = this->Diag_->getLocalViewHost(Tpetra::Access::ReadOnly);
    ISC d         = (static_cast<ISC>(dampingFactor)) / diagView(LRID, 0);
    for (size_t m = 0; m < numVecs; m++) {
      // ISC x = X(LRID, m);
      ISC r = X(LRID, m);
      for (size_type k = rowmap(LRID); k < rowmap(LRID + 1); k++) {
        const LO col = entries(k);
        r -= values(k) * Y2(col, m);
      }
 
      ISC newy = r * d;
      Y2(LRID, m) += newy;
    }
  } else if (!this->inputCrsMatrix_.is_null() &&
             std::is_same<typename crs_matrix_type::device_type::memory_space, Kokkos::HostSpace>::value) {
    // Use the KokkosSparse internal matrix for low-overhead values/indices access
    // But, can only do this if the matrix is accessible directly from host, since it's not a DualView
    using container_exec_space = typename ContainerImpl<MatrixType, LocalScalarType>::crs_matrix_type::execution_space;
    container_exec_space().fence();
    auto localA                   = this->inputCrsMatrix_->getLocalMatrixHost();
    using size_type               = typename crs_matrix_type::local_matrix_host_type::size_type;
    const auto& rowmap            = localA.graph.row_map;
    const auto& entries           = localA.graph.entries;
    const auto& values            = localA.values;
    ArrayView<const LO> blockRows = this->getBlockRows(i);
    for (size_t j = 0; j < size_t(blockRows.size()); j++) {
      const LO row = blockRows[j];
      for (size_t m = 0; m < numVecs; m++) {
        ISC r = X(row, m);
        for (size_type k = rowmap(row); k < rowmap(row + 1); k++) {
          const LO col = entries(k);
          r -= values(k) * Y2(col, m);
        }
        Resid(row, m) = r;
      }
    }
    // solve with this block
    //
    // Note: I'm abusing the ordering information, knowing that X/Y
    // and Y2 have the same ordering for on-proc unknowns.
    //
    // Note: Add flop counts for inverse apply
    apply(Resid, Y2, i, Teuchos::NO_TRANS, dampingFactor, one);
  } else {
    // Either a point-indexed block matrix, or a normal row matrix
    // that doesn't support getLocalMatrix
    ArrayView<const LO> blockRows = this->getBlockRows(i);
    for (size_t j = 0; j < size_t(blockRows.size()); j++) {
      const LO row = blockRows[j];
      auto rowView = getInputRowView(row);
      for (size_t m = 0; m < numVecs; m++) {
        Resid(row, m) = X(row, m);
        for (size_t k = 0; k < rowView.size(); ++k) {
          const LO col = rowView.ind(k);
          Resid(row, m) -= rowView.val(k) * Y2(col, m);
        }
      }
    }
    // solve with this block
    //
    // Note: I'm abusing the ordering information, knowing that X/Y
    // and Y2 have the same ordering for on-proc unknowns.
    //
    // Note: Add flop counts for inverse apply
    apply(Resid, Y2, i, Teuchos::NO_TRANS, dampingFactor, one);
  }
}
 
template <class MatrixType>
void Container<MatrixType>::
    DoGaussSeidel(ConstHostView X, HostView Y, HostView Y2, SC dampingFactor) const {
  using Teuchos::Array;
  using Teuchos::ArrayRCP;
  using Teuchos::ArrayView;
  using Teuchos::Ptr;
  using Teuchos::RCP;
  using Teuchos::rcp;
  using Teuchos::rcpFromRef;
  // This function just extracts the diagonal if it hasn't already.
  getMatDiag();
  auto numVecs = X.extent(1);
  // X = RHS, Y = initial guess
  HostView Resid("", X.extent(0), X.extent(1));
  for (LO i = 0; i < numBlocks_; i++) {
    DoGSBlock(X, Y, Y2, Resid, dampingFactor, i);
  }
  if (IsParallel_) {
    auto numMyRows = inputMatrix_->getLocalNumRows();
    for (size_t m = 0; m < numVecs; ++m) {
      for (size_t i = 0; i < numMyRows * bcrsBlockSize_; ++i) {
        Y(i, m) = Y2(i, m);
      }
    }
  }
}
 
template <class MatrixType>
void Container<MatrixType>::
    DoSGS(ConstHostView X, HostView Y, HostView Y2, SC dampingFactor) const {
  // X = RHS, Y = initial guess
  using Teuchos::Array;
  using Teuchos::ArrayRCP;
  using Teuchos::ArrayView;
  using Teuchos::Ptr;
  using Teuchos::ptr;
  using Teuchos::RCP;
  using Teuchos::rcp;
  using Teuchos::rcpFromRef;
  auto numVecs = X.extent(1);
  HostView Resid("", X.extent(0), X.extent(1));
  // Forward Sweep
  for (LO i = 0; i < numBlocks_; i++) {
    DoGSBlock(X, Y, Y2, Resid, dampingFactor, i);
  }
  static_assert(std::is_signed<LO>::value,
                "Local ordinal must be signed (unsigned breaks reverse iteration to 0)");
  // Reverse Sweep
  for (LO i = numBlocks_ - 1; i >= 0; --i) {
    DoGSBlock(X, Y, Y2, Resid, dampingFactor, i);
  }
  if (IsParallel_) {
    auto numMyRows = inputMatrix_->getLocalNumRows();
    for (size_t m = 0; m < numVecs; ++m) {
      for (size_t i = 0; i < numMyRows * bcrsBlockSize_; ++i) {
        Y(i, m) = Y2(i, m);
      }
    }
  }
}
 
template <class MatrixType>
void Container<MatrixType>::
    clearBlocks() {
  numBlocks_ = 0;
  blockRows_.clear();
  blockSizes_.clear();
  blockOffsets_.clear();
  Diag_ = Teuchos::null;  // Diag_ will be recreated if needed
}
 
// Implementation of Ifpack2::ContainerImpl
 
template <class MatrixType, class LocalScalarType>
ContainerImpl<MatrixType, LocalScalarType>::
    ContainerImpl(
        const Teuchos::RCP<const row_matrix_type>& matrix,
        const Teuchos::Array<Teuchos::Array<LO>>& partitions,
        bool pointIndexed)
  : Container<MatrixType>(matrix, partitions, pointIndexed) {}
 
template <class MatrixType, class LocalScalarType>
ContainerImpl<MatrixType, LocalScalarType>::
    ~ContainerImpl() {}
 
template <class MatrixType, class LocalScalarType>
void ContainerImpl<MatrixType, LocalScalarType>::
    setParameters(const Teuchos::ParameterList& List) {}
 
template <class MatrixType, class LocalScalarType>
void ContainerImpl<MatrixType, LocalScalarType>::
    applyInverseJacobi(const mv_type& /* X */, mv_type& /* Y */,
                       SC /*dampingFactor*/,
                       bool /* zeroStartingSolution = false */,
                       int /* numSweeps = 1 */) const {
  TEUCHOS_TEST_FOR_EXCEPT_MSG(true, "Not implemented.");
}
 
template <class MatrixType, class LocalScalarType>
void ContainerImpl<MatrixType, LocalScalarType>::
    applyMV(const mv_type& X, mv_type& Y) const {
  ConstHostView XView = X.getLocalViewHost(Tpetra::Access::ReadOnly);
  HostView YView      = Y.getLocalViewHost(Tpetra::Access::ReadWrite);
  this->apply(XView, YView, 0);
}
 
template <class MatrixType, class LocalScalarType>
void ContainerImpl<MatrixType, LocalScalarType>::
    weightedApplyMV(const mv_type& X,
                    mv_type& Y,
                    vector_type& W) const {
  ConstHostView XView = X.getLocalViewHost(Tpetra::Access::ReadOnly);
  HostView YView      = Y.getLocalViewHost(Tpetra::Access::ReadWrite);
  ConstHostView WView = W.getLocalViewHost(Tpetra::Access::ReadOnly);
  weightedApply(XView, YView, WView, 0);
}
 
template <class MatrixType, class LocalScalarType>
std::string ContainerImpl<MatrixType, LocalScalarType>::
    getName() {
  return "Generic";
}
 
template <class MatrixType, class LocalScalarType>
void ContainerImpl<MatrixType, LocalScalarType>::
    solveBlock(ConstHostSubviewLocal /*X*/,
               HostSubviewLocal /*Y*/,
               int /*blockIndex*/,
               Teuchos::ETransp /*mode*/,
               const LSC /*alpha*/,
               const LSC /*beta*/) const {
  TEUCHOS_TEST_FOR_EXCEPT_MSG(true, "Not implemented.");
}
 
template <class MatrixType, class LocalScalarType>
typename ContainerImpl<MatrixType, LocalScalarType>::LO
ContainerImpl<MatrixType, LocalScalarType>::
    translateRowToCol(LO row) {
  LO LO_INVALID                = Teuchos::OrdinalTraits<LO>::invalid();
  GO GO_INVALID                = Teuchos::OrdinalTraits<GO>::invalid();
  const map_type& globalRowMap = *(this->inputMatrix_->getRowMap());
  const map_type& globalColMap = *(this->inputMatrix_->getColMap());
  LO rowLID                    = row;
  LO dofOffset                 = 0;
  if (this->pointIndexed_) {
    rowLID    = row / this->bcrsBlockSize_;
    dofOffset = row % this->bcrsBlockSize_;
  }
  GO diagGID = globalRowMap.getGlobalElement(rowLID);
  TEUCHOS_TEST_FOR_EXCEPTION(
      diagGID == GO_INVALID,
      std::runtime_error,
      "Ifpack2::Container::translateRowToCol: "
      "On process "
          << this->inputMatrix_->getRowMap()->getComm()->getRank() << ", at least one row index in the set of local "
                                                                      "row indices given to the constructor is not a valid local row index in "
                                                                      "the input matrix's row Map on this process.  This should be impossible "
                                                                      "because the constructor checks for this case.  Here is the complete set "
                                                                      "of invalid local row indices: "
          << rowLID << ".  "
                       "Please report this bug to the Ifpack2 developers.");
  // now, can translate diagGID (both a global row AND global col ID) to local column
  LO colLID = globalColMap.getLocalElement(diagGID);
  TEUCHOS_TEST_FOR_EXCEPTION(
      colLID == LO_INVALID,
      std::runtime_error,
      "Ifpack2::Container::translateRowToCol: "
      "On process "
          << this->inputMatrix_->getRowMap()->getComm()->getRank() << ", "
                                                                      "at least one row index in the set of row indices given to the constructor "
                                                                      "does not have a corresponding column index in the input matrix's column "
                                                                      "Map.  This probably means that the column(s) in question is/are empty on "
                                                                      "this process, which would make the submatrix to extract structurally "
                                                                      "singular. The invalid global column index is "
          << diagGID << ".");
  // colLID could identify a block column - translate to split column if needed
  if (this->pointIndexed_)
    return colLID * this->bcrsBlockSize_ + dofOffset;
  return colLID;
}
 
template <class MatrixType, class LocalScalarType>
void ContainerImpl<MatrixType, LocalScalarType>::
    apply(ConstHostView X,
          HostView Y,
          int blockIndex,
          Teuchos::ETransp mode,
          SC alpha,
          SC beta) const {
  using Teuchos::ArrayView;
  using Teuchos::as;
  using Teuchos::RCP;
  using Teuchos::rcp;
 
  // The local operator might have a different Scalar type than
  // MatrixType.  This means that we might have to convert X and Y to
  // the Tpetra::MultiVector specialization that the local operator
  // wants.  This class' X_ and Y_ internal fields are of the right
  // type for the local operator, so we can use those as targets.
 
  Details::MultiVectorLocalGatherScatter<mv_type, local_mv_type> mvgs;
 
  TEUCHOS_TEST_FOR_EXCEPTION(
      !this->IsComputed_, std::runtime_error,
      "Ifpack2::Container::apply: "
      "You must have called the compute() method before you may call apply().  "
      "You may call the apply() method as many times as you want after calling "
      "compute() once, but you must have called compute() at least once.");
 
  const size_t numVecs = X.extent(1);
 
  if (numVecs == 0) {
    return;  // done! nothing to do
  }
 
  // The local operator works on a permuted subset of the local parts
  // of X and Y.  The subset and permutation are defined by the index
  // array returned by getBlockRows().  If the permutation is trivial
  // and the subset is exactly equal to the local indices, then we
  // could use the local parts of X and Y exactly, without needing to
  // permute.  Otherwise, we have to use temporary storage to permute
  // X and Y.  For now, we always use temporary storage.
  //
  // Create temporary permuted versions of the input and output.
  // (Re)allocate X_ and/or Y_ only if necessary.  We'll use them to
  // store the permuted versions of X resp. Y.  Note that X_local has
  // the domain Map of the operator, which may be a permuted subset of
  // the local Map corresponding to X.getMap().  Similarly, Y_local
  // has the range Map of the operator, which may be a permuted subset
  // of the local Map corresponding to Y.getMap().  numRows_ here
  // gives the number of rows in the row Map of the local Inverse_
  // operator.
  //
  // FIXME (mfh 20 Aug 2013) There might be an implicit assumption
  // here that the row Map and the range Map of that operator are
  // the same.
  //
  // FIXME (mfh 20 Aug 2013) This "local permutation" functionality
  // really belongs in Tpetra.
 
  if (X_localBlocks_.size() == 0 || X.extent(1) != X_local_.extent(1)) {
    // need to resize (or create for the first time) the three scratch arrays
    X_localBlocks_.clear();
    Y_localBlocks_.clear();
    X_localBlocks_.reserve(this->numBlocks_);
    Y_localBlocks_.reserve(this->numBlocks_);
 
    X_local_ = HostViewLocal("X_local", this->blockRows_.size() * this->scalarsPerRow_, numVecs);
    Y_local_ = HostViewLocal("Y_local", this->blockRows_.size() * this->scalarsPerRow_, numVecs);
 
    // create all X_local and Y_local managed Views at once, are
    // reused in subsequent apply() calls
    for (int i = 0; i < this->numBlocks_; i++) {
      auto blockBounds = std::make_pair(this->blockOffsets_[i] * this->scalarsPerRow_,
                                        (this->blockOffsets_[i] + this->blockSizes_[i]) * this->scalarsPerRow_);
      X_localBlocks_.emplace_back(X_local_, blockBounds, Kokkos::ALL());
      Y_localBlocks_.emplace_back(Y_local_, blockBounds, Kokkos::ALL());
    }
  }
 
  const ArrayView<const LO> blockRows = this->getBlockRows(blockIndex);
 
  if (this->scalarsPerRow_ == 1)
    mvgs.gatherViewToView(X_localBlocks_[blockIndex], X, blockRows);
  else
    mvgs.gatherViewToViewBlock(X_localBlocks_[blockIndex], X, blockRows, this->scalarsPerRow_);
 
  // We must gather the contents of the output multivector Y even on
  // input to solveBlock(), since the inverse operator might use it as
  // an initial guess for a linear solve.  We have no way of knowing
  // whether it does or does not.
 
  if (this->scalarsPerRow_ == 1)
    mvgs.gatherViewToView(Y_localBlocks_[blockIndex], Y, blockRows);
  else
    mvgs.gatherViewToViewBlock(Y_localBlocks_[blockIndex], Y, blockRows, this->scalarsPerRow_);
 
  // Apply the local operator:
  // Y_local := beta*Y_local + alpha*M^{-1}*X_local
  this->solveBlock(X_localBlocks_[blockIndex], Y_localBlocks_[blockIndex], blockIndex, mode,
                   LSC(alpha), LSC(beta));
 
  // Scatter the permuted subset output vector Y_local back into the
  // original output multivector Y.
  if (this->scalarsPerRow_ == 1)
    mvgs.scatterViewToView(Y, Y_localBlocks_[blockIndex], blockRows);
  else
    mvgs.scatterViewToViewBlock(Y, Y_localBlocks_[blockIndex], blockRows, this->scalarsPerRow_);
}
 
template <class MatrixType, class LocalScalarType>
void ContainerImpl<MatrixType, LocalScalarType>::
    weightedApply(ConstHostView X,
                  HostView Y,
                  ConstHostView D,
                  int blockIndex,
                  Teuchos::ETransp mode,
                  SC alpha,
                  SC beta) const {
  using std::endl;
  using Teuchos::ArrayRCP;
  using Teuchos::ArrayView;
  using Teuchos::Ptr;
  using Teuchos::ptr;
  using Teuchos::Range1D;
  using Teuchos::RCP;
  using Teuchos::rcp;
  using Teuchos::rcp_const_cast;
  using STS = Teuchos::ScalarTraits<SC>;
 
  // The local operator template parameter might have a different
  // Scalar type than MatrixType.  This means that we might have to
  // convert X and Y to the Tpetra::MultiVector specialization that
  // the local operator wants.  This class' X_ and Y_ internal fields
  // are of the right type for the local operator, so we can use those
  // as targets.
 
  const char prefix[] = "Ifpack2::Container::weightedApply: ";
  TEUCHOS_TEST_FOR_EXCEPTION(
      !this->IsComputed_, std::runtime_error, prefix << "You must have called the "
                                                        "compute() method before you may call this method.  You may call "
                                                        "weightedApply() as many times as you want after calling compute() once, "
                                                        "but you must have called compute() at least once first.");
 
  // bmk 7-2019: BlockRelaxation already checked this, but if that changes...
  TEUCHOS_TEST_FOR_EXCEPTION(
      this->scalarsPerRow_ > 1, std::logic_error, prefix << "Use of block rows isn't allowed "
                                                            "in overlapping Jacobi (the only method that uses weightedApply");
 
  const size_t numVecs = X.extent(1);
 
  TEUCHOS_TEST_FOR_EXCEPTION(
      X.extent(1) != Y.extent(1), std::runtime_error,
      prefix << "X and Y have different numbers of vectors (columns).  X has "
             << X.extent(1) << ", but Y has " << Y.extent(1) << ".");
 
  if (numVecs == 0) {
    return;  // done! nothing to do
  }
 
  const size_t numRows = this->blockSizes_[blockIndex];
 
  // The local operator works on a permuted subset of the local parts
  // of X and Y.  The subset and permutation are defined by the index
  // array returned by getBlockRows().  If the permutation is trivial
  // and the subset is exactly equal to the local indices, then we
  // could use the local parts of X and Y exactly, without needing to
  // permute.  Otherwise, we have to use temporary storage to permute
  // X and Y.  For now, we always use temporary storage.
  //
  // Create temporary permuted versions of the input and output.
  // (Re)allocate X_ and/or Y_ only if necessary.  We'll use them to
  // store the permuted versions of X resp. Y.  Note that X_local has
  // the domain Map of the operator, which may be a permuted subset of
  // the local Map corresponding to X.getMap().  Similarly, Y_local
  // has the range Map of the operator, which may be a permuted subset
  // of the local Map corresponding to Y.getMap().  numRows_ here
  // gives the number of rows in the row Map of the local operator.
  //
  // FIXME (mfh 20 Aug 2013) There might be an implicit assumption
  // here that the row Map and the range Map of that operator are
  // the same.
  //
  // FIXME (mfh 20 Aug 2013) This "local permutation" functionality
  // really belongs in Tpetra.
  if (X_localBlocks_.size() == 0 || X.extent(1) != X_local_.extent(1)) {
    // need to resize (or create for the first time) the three scratch arrays
    X_localBlocks_.clear();
    Y_localBlocks_.clear();
    X_localBlocks_.reserve(this->numBlocks_);
    Y_localBlocks_.reserve(this->numBlocks_);
 
    X_local_ = HostViewLocal("X_local", this->blockRows_.size() * this->scalarsPerRow_, numVecs);
    Y_local_ = HostViewLocal("Y_local", this->blockRows_.size() * this->scalarsPerRow_, numVecs);
 
    // create all X_local and Y_local managed Views at once, are
    // reused in subsequent apply() calls
    for (int i = 0; i < this->numBlocks_; i++) {
      auto blockBounds = std::make_pair(this->blockOffsets_[i] * this->scalarsPerRow_,
                                        (this->blockOffsets_[i] + this->blockSizes_[i]) * this->scalarsPerRow_);
      X_localBlocks_.emplace_back(X_local_, blockBounds, Kokkos::ALL());
      Y_localBlocks_.emplace_back(Y_local_, blockBounds, Kokkos::ALL());
    }
  }
  if (int(weightedApplyScratch_.extent(0)) != 3 * this->maxBlockSize_ ||
      weightedApplyScratch_.extent(1) != numVecs) {
    weightedApplyScratch_ = HostViewLocal("weightedApply scratch", 3 * this->maxBlockSize_, numVecs);
  }
 
  ArrayView<const LO> blockRows = this->getBlockRows(blockIndex);
 
  Details::MultiVectorLocalGatherScatter<mv_type, local_mv_type> mvgs;
 
  // note: BlockCrs w/ weighted Jacobi isn't allowed, so no need to use block gather/scatter
  mvgs.gatherViewToView(X_localBlocks_[blockIndex], X, blockRows);
  // We must gather the output multivector Y even on input to
  // solveBlock(), since the local operator might use it as an initial
  // guess for a linear solve.  We have no way of knowing whether it
  // does or does not.
 
  mvgs.gatherViewToView(Y_localBlocks_[blockIndex], Y, blockRows);
 
  // Apply the diagonal scaling D to the input X.  It's our choice
  // whether the result has the original input Map of X, or the
  // permuted subset Map of X_local.  If the latter, we also need to
  // gather D into the permuted subset Map.  We choose the latter, to
  // save memory and computation.  Thus, we do the following:
  //
  // 1. Gather D into a temporary vector D_local.
  // 2. Create a temporary X_scaled to hold diag(D_local) * X_local.
  // 3. Compute X_scaled := diag(D_loca) * X_local.
  auto maxBS = this->maxBlockSize_;
  auto bs    = this->blockSizes_[blockIndex] * this->scalarsPerRow_;
 
  HostSubviewLocal D_local(weightedApplyScratch_, std::make_pair(0, bs), std::make_pair(0, 1));
  mvgs.gatherViewToView(D_local, D, blockRows);
  HostSubviewLocal X_scaled(weightedApplyScratch_, std::make_pair(maxBS, maxBS + bs), Kokkos::ALL());
  for (size_t j = 0; j < numVecs; j++)
    for (size_t i = 0; i < numRows; i++)
      X_scaled(i, j) = X_localBlocks_[blockIndex](i, j) * D_local(i, 0);
 
  HostSubviewLocal Y_temp(weightedApplyScratch_, std::make_pair(maxBS * 2, maxBS * 2 + bs), Kokkos::ALL());
  // Apply the local operator: Y_temp := M^{-1} * X_scaled
  this->solveBlock(X_scaled, Y_temp, blockIndex, mode, STS::one(), STS::zero());
  // Y_local := beta * Y_local + alpha * diag(D_local) * Y_temp.
  //
  // Note that we still use the permuted subset scaling D_local here,
  // because Y_temp has the same permuted subset Map.  That's good, in
  // fact, because it's a subset: less data to read and multiply.
  LISC a = alpha;
  LISC b = beta;
  for (size_t j = 0; j < numVecs; j++)
    for (size_t i = 0; i < numRows; i++)
      Y_localBlocks_[blockIndex](i, j) = b * Y_localBlocks_[blockIndex](i, j) + a * Y_temp(i, j) * D_local(i, 0);
 
  // Copy the permuted subset output vector Y_local into the original
  // output multivector Y.
  mvgs.scatterViewToView(Y, Y_localBlocks_[blockIndex], blockRows);
}
 
template <class MatrixType, class LocalScalarType>
Details::StridedRowView<
    typename ContainerImpl<MatrixType, LocalScalarType>::SC,
    typename ContainerImpl<MatrixType, LocalScalarType>::LO,
    typename ContainerImpl<MatrixType, LocalScalarType>::GO,
    typename ContainerImpl<MatrixType, LocalScalarType>::NO>
ContainerImpl<MatrixType, LocalScalarType>::
    getInputRowView(LO row) const {
  typedef typename MatrixType::nonconst_local_inds_host_view_type nonconst_local_inds_host_view_type;
  typedef typename MatrixType::nonconst_values_host_view_type nonconst_values_host_view_type;
 
  typedef typename MatrixType::local_inds_host_view_type local_inds_host_view_type;
  typedef typename MatrixType::values_host_view_type values_host_view_type;
  using IST = typename row_matrix_type::impl_scalar_type;
 
  if (this->hasBlockCrs_) {
    using h_inds_type = typename block_crs_matrix_type::local_inds_host_view_type;
    using h_vals_type = typename block_crs_matrix_type::values_host_view_type;
    h_inds_type colinds;
    h_vals_type values;
    this->inputBlockMatrix_->getLocalRowView(row / this->bcrsBlockSize_, colinds, values);
    size_t numEntries = colinds.size();
    // CMS: Can't say I understand what this really does
    // return StridedRowView(values + row % this->bcrsBlockSize_, colinds, this->bcrsBlockSize_, numEntries * this->bcrsBlockSize_);
    h_vals_type subvals = Kokkos::subview(values, std::pair<size_t, size_t>(row % this->bcrsBlockSize_, values.size()));
    return StridedRowView(subvals, colinds, this->bcrsBlockSize_, numEntries * this->bcrsBlockSize_);
  } else if (!this->inputMatrix_->supportsRowViews()) {
    size_t maxEntries = this->inputMatrix_->getLocalMaxNumRowEntries();
    Teuchos::Array<LO> inds(maxEntries);
    Teuchos::Array<SC> vals(maxEntries);
    nonconst_local_inds_host_view_type inds_v(inds.data(), maxEntries);
    nonconst_values_host_view_type vals_v(reinterpret_cast<IST*>(vals.data()), maxEntries);
    size_t numEntries;
    this->inputMatrix_->getLocalRowCopy(row, inds_v, vals_v, numEntries);
    vals.resize(numEntries);
    inds.resize(numEntries);
    return StridedRowView(vals, inds);
  } else {
    // CMS - This is dangerous and might not work.
    local_inds_host_view_type colinds;
    values_host_view_type values;
    this->inputMatrix_->getLocalRowView(row, colinds, values);
    return StridedRowView(values, colinds, 1, colinds.size());
  }
}
 
template <class MatrixType, class LocalScalarType>
void ContainerImpl<MatrixType, LocalScalarType>::
    clearBlocks() {
  X_localBlocks_.clear();
  Y_localBlocks_.clear();
  X_local_ = HostViewLocal();
  Y_local_ = HostViewLocal();
  Container<MatrixType>::clearBlocks();
}
 
namespace Details {
 
// Implementation of Ifpack2::Details::StridedRowView
template <class Scalar, class LocalOrdinal, class GlobalOrdinal, class Node>
StridedRowView<Scalar, LocalOrdinal, GlobalOrdinal, Node>::
    StridedRowView(h_vals_type vals_, h_inds_type inds_, int blockSize_, size_t nnz_)
  : vals(vals_)
  , inds(inds_)
  , blockSize(blockSize_)
  , nnz(nnz_) {}
 
template <class Scalar, class LocalOrdinal, class GlobalOrdinal, class Node>
StridedRowView<Scalar, LocalOrdinal, GlobalOrdinal, Node>::
    StridedRowView(Teuchos::Array<SC>& vals_, Teuchos::Array<LO>& inds_)
  : vals()
  , inds()
  , blockSize(1)
  , nnz(vals_.size()) {
  valsCopy.swap(vals_);
  indsCopy.swap(inds_);
}
 
template <class Scalar, class LocalOrdinal, class GlobalOrdinal, class Node>
Scalar StridedRowView<Scalar, LocalOrdinal, GlobalOrdinal, Node>::
    val(size_t i) const {
  if (Ifpack2::Details::Behavior::debug()) {
    TEUCHOS_TEST_FOR_EXCEPTION(i >= nnz, std::runtime_error,
                               "Out-of-bounds access into Ifpack2::Container::StridedRowView");
  }
  if (vals.size() > 0) {
    if (blockSize == 1)
      return vals[i];
    else
      return vals[i * blockSize];
  } else
    return valsCopy[i];
}
 
template <class Scalar, class LocalOrdinal, class GlobalOrdinal, class Node>
LocalOrdinal StridedRowView<Scalar, LocalOrdinal, GlobalOrdinal, Node>::
    ind(size_t i) const {
  if (Ifpack2::Details::Behavior::debug()) {
    TEUCHOS_TEST_FOR_EXCEPTION(i >= nnz, std::runtime_error,
                               "Out-of-bounds access into Ifpack2::Container::StridedRowView");
  }
  // inds is smaller than vals by a factor of the block size (dofs/node)
  if (inds.size() > 0) {
    if (blockSize == 1)
      return inds[i];
    else
      return inds[i / blockSize] * blockSize + i % blockSize;
  } else
    return indsCopy[i];
}
 
template <class Scalar, class LocalOrdinal, class GlobalOrdinal, class Node>
size_t StridedRowView<Scalar, LocalOrdinal, GlobalOrdinal, Node>::
    size() const {
  return nnz;
}
}  // namespace Details
 
}  // namespace Ifpack2
 
template <class MatrixType>
std::ostream& operator<<(std::ostream& os, const Ifpack2::Container<MatrixType>& obj) {
  return obj.print(os);
}
 
#define IFPACK2_CONTAINER_INSTANT(S, LO, GO, N)                              \
  template class Ifpack2::Container<Tpetra::RowMatrix<S, LO, GO, N>>;        \
  template class Ifpack2::ContainerImpl<Tpetra::RowMatrix<S, LO, GO, N>, S>; \
  template class Ifpack2::Details::StridedRowView<S, LO, GO, N>;             \
  template std::ostream& operator<< <Tpetra::RowMatrix<S, LO, GO, N>>(       \
      std::ostream& os, const Ifpack2::Container<Tpetra::RowMatrix<S, LO, GO, N>>& obj);
 
#endif