MueLu_AggregationPhase2aAlgorithm_def.hpp

Go to the documentation of this file.

// @HEADER
//
// ***********************************************************************
//
//        MueLu: A package for multigrid based preconditioning
//                  Copyright 2012 Sandia Corporation
//
// Under the terms of Contract DE-AC04-94AL85000 with Sandia Corporation,
// the U.S. Government retains certain rights in this software.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// 1. Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
//
// 3. Neither the name of the Corporation nor the names of the
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY SANDIA CORPORATION "AS IS" AND ANY
// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL SANDIA CORPORATION OR THE
// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// Questions? Contact
//                    Jonathan Hu       (jhu@sandia.gov)
//                    Andrey Prokopenko (aprokop@sandia.gov)
//                    Ray Tuminaro      (rstumin@sandia.gov)
//
// ***********************************************************************
//
// @HEADER
#ifndef MUELU_AGGREGATIONPHASE2AALGORITHM_DEF_HPP_
#define MUELU_AGGREGATIONPHASE2AALGORITHM_DEF_HPP_


#include <Teuchos_Comm.hpp>
#include <Teuchos_CommHelpers.hpp>

#include <Xpetra_Vector.hpp>

#include "MueLu_AggregationPhase2aAlgorithm_decl.hpp"

#include "MueLu_GraphBase.hpp"
#include "MueLu_Aggregates.hpp"
#include "MueLu_Exceptions.hpp"
#include "MueLu_Monitor.hpp"

namespace MueLu {

  template <class LocalOrdinal, class GlobalOrdinal, class Node>
  void AggregationPhase2aAlgorithm<LocalOrdinal, GlobalOrdinal, Node>::BuildAggregates(const ParameterList& params, const GraphBase& graph, Aggregates& aggregates, std::vector<unsigned>& aggStat, LO& numNonAggregatedNodes) const {
    Monitor m(*this, "BuildAggregates");

    int minNodesPerAggregate = params.get<int>("aggregation: min agg size");
    int maxNodesPerAggregate = params.get<int>("aggregation: max agg size");

    const LO  numRows = graph.GetNodeNumVertices();
    const int myRank  = graph.GetComm()->getRank();

    ArrayRCP<LO> vertex2AggId = aggregates.GetVertex2AggId()->getDataNonConst(0);
    ArrayRCP<LO> procWinner   = aggregates.GetProcWinner()  ->getDataNonConst(0);

    LO numLocalAggregates = aggregates.GetNumAggregates();

    LO numLocalNodes      = procWinner.size();
    LO numLocalAggregated = numLocalNodes - numNonAggregatedNodes;

    const double aggFactor = 0.5;
    double       factor    = as<double>(numLocalAggregated)/(numLocalNodes+1);
    factor = pow(factor, aggFactor);

    int              aggIndex = -1;
    size_t           aggSize  =  0;
    std::vector<int> aggList(graph.getNodeMaxNumRowEntries());

    for (LO rootCandidate = 0; rootCandidate < numRows; rootCandidate++) {
      if (aggStat[rootCandidate] != READY)
        continue;

      aggSize = 0;

      ArrayView<const LocalOrdinal> neighOfINode = graph.getNeighborVertices(rootCandidate);

      LO numNeighbors = 0;
      for (int j = 0; j < neighOfINode.size(); j++) {
        LO neigh = neighOfINode[j];

        if (neigh != rootCandidate) {
          if (graph.isLocalNeighborVertex(neigh) && aggStat[neigh] == READY) {
            // If aggregate size does not exceed max size, add node to the tentative aggregate
            // NOTE: We do not exit the loop over all neighbours since we have still
            //       to count all aggregated neighbour nodes for the aggregation criteria
            // NOTE: We check here for the maximum aggregation size. If we would do it below
            //       with all the other check too big aggregates would not be accepted at all.
            if (aggSize < as<size_t>(maxNodesPerAggregate))
              aggList[aggSize++] = neigh;
          }

          numNeighbors++;
        }
      }

      // NOTE: ML uses a hardcoded value 3 instead of MinNodesPerAggregate
      if (aggSize > as<size_t>(minNodesPerAggregate) &&
          aggSize > factor*numNeighbors) {
        // Accept new aggregate
        // rootCandidate becomes the root of the newly formed aggregate
        aggregates.SetIsRoot(rootCandidate);
        aggIndex = numLocalAggregates++;

        for (size_t k = 0; k < aggSize; k++) {
          aggStat     [aggList[k]] = AGGREGATED;
          vertex2AggId[aggList[k]] = aggIndex;
          procWinner  [aggList[k]] = myRank;
        }

        numNonAggregatedNodes -= aggSize;
      }
    }

    // update aggregate object
    aggregates.SetNumAggregates(numLocalAggregates);
  }

} // end namespace

#endif /* MUELU_AGGREGATIONPHASE2AALGORITHM_DEF_HPP_ */