MueLu_MatrixFreeTentativeP_kokkos_def.hpp

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#ifndef MUELU_MATRIXFREETENTATIVEP_KOKKOS_DEF_HPP
#define MUELU_MATRIXFREETENTATIVEP_KOKKOS_DEF_HPP

#include "MueLu_MatrixFreeTentativeP_kokkos_decl.hpp"

#include "MueLu_Aggregates_kokkos.hpp"
#include "MueLu_Level.hpp"
#include "MueLu_MasterList.hpp"
#include "MueLu_PerfUtils.hpp"
#include "MueLu_PFactory.hpp"
#include "MueLu_Monitor.hpp"
#include "MueLu_Utilities_kokkos.hpp"

#include <KokkosCompat_ClassicNodeAPI_Wrapper.hpp>

#include "Teuchos_ScalarTraits.hpp"

namespace MueLu {

  // compute Y = alpha*R*X + beta*Y
  template <class Scalar, class LocalOrdinal, class GlobalOrdinal, class DeviceType>
  void MatrixFreeTentativeP_kokkos<Scalar,LocalOrdinal,GlobalOrdinal,Kokkos::Compat::KokkosDeviceWrapperNode<DeviceType>>::apply(const MultiVector &X,
                                          MultiVector &Y,
                                          Teuchos::ETransp mode,
                                          Scalar alpha,
                                          Scalar beta) const {

    using impl_scalar_type = typename Kokkos::ArithTraits<Scalar>::val_type;
    impl_scalar_type implAlpha = alpha;

    // Step 1: Y*=beta*Y, setup necessary structures
    Y.scale(beta);

    // TODO: probably smarter to sqrt the whole aggSizes once, but may be slower if it's done in a separate kernel launch?
    typename Aggregates_kokkos::aggregates_sizes_type::const_type aggSizes = aggregates_->ComputeAggregateSizes();

    auto kokkos_view_X = X.getDeviceLocalView(Xpetra::Access::ReadOnly);
    auto kokkos_view_Y = Y.getDeviceLocalView(Xpetra::Access::ReadWrite);
    LO numCols = kokkos_view_X.extent(1);

    if(mode == Teuchos::TRANS) { // if we're in restrictor mode
      auto vertex2AggId = aggregates_->GetVertex2AggId();
      auto vertex2AggIdView = vertex2AggId->getDeviceLocalView(Xpetra::Access::ReadOnly);
      LO numNodes = kokkos_view_X.extent(0);

      // Step 2: Compute Y=Y+alpha*R*X
      // recall R*X is an average of X over aggregates
      Kokkos::parallel_for("MueLu:MatrixFreeTentativeR_kokkos:apply", md_range_type({0,0},{numCols,numNodes}),
        KOKKOS_LAMBDA(const int colIdx, const int NodeIdx) {
          LO aggIdx = vertex2AggIdView(NodeIdx,0);
          if(aggIdx != -1) { // depending on maps, vertex2agg
            Kokkos::atomic_add(&kokkos_view_Y(aggIdx,colIdx),implAlpha*kokkos_view_X(NodeIdx,colIdx)/Kokkos::sqrt(aggSizes(aggIdx)));
          }
        });
    } else { // if we're in prolongator mode
      const auto vertex2Agg = aggregates_->GetVertex2AggId();
      auto vertex2AggView = vertex2Agg->getDeviceLocalView(Xpetra::Access::ReadOnly);
      LO numNodes = kokkos_view_Y.extent(0);

      // Step 2: Compute Y=Y+alpha*P*X
      // recall P*X is essentially injection of X, but sum if a node belongs to multiple aggregates
      Kokkos::parallel_for("MueLu:MatrixFreeTentativeP_kokkos:apply", md_range_type({0,0},{numCols,numNodes}),
        KOKKOS_LAMBDA(const int colIdx, const int fineIdx) {
          LO aggIdx = vertex2AggView(fineIdx,0);
          kokkos_view_Y(fineIdx,colIdx) += implAlpha*kokkos_view_X(aggIdx,colIdx)/Kokkos::sqrt(aggSizes(aggIdx));
        });
    }
  }

  // I don't care
  template <class Scalar, class LocalOrdinal, class GlobalOrdinal, class DeviceType>
  void MatrixFreeTentativeP_kokkos<Scalar,LocalOrdinal,GlobalOrdinal,Kokkos::Compat::KokkosDeviceWrapperNode<DeviceType>>::residual(const MultiVector &X, const MultiVector &B, MultiVector &R) const {
    TEUCHOS_TEST_FOR_EXCEPTION(true,Exceptions::RuntimeError,"MatrixFreeTentativeP residual would make no sense as the operator is not square!");
  }

} //namespace MueLu

#define MUELU_MATRIXFREETENTATIVEP_KOKKOS_SHORT
#endif // MUELU_MATRIXFREETENTATIVEP_KOKKOS_DEF_HPP