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MueLu_AggregationPhase3Algorithm_kokkos_def.hpp
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46 #ifndef MUELU_AGGREGATIONPHASE3ALGORITHM_KOKKOS_DEF_HPP
47 #define MUELU_AGGREGATIONPHASE3ALGORITHM_KOKKOS_DEF_HPP
48 
49 #ifdef HAVE_MUELU_KOKKOS_REFACTOR
50 
51 #include <Teuchos_Comm.hpp>
52 #include <Teuchos_CommHelpers.hpp>
53 
54 #include <Xpetra_Vector.hpp>
55 
57 
58 #include "MueLu_Aggregates_kokkos.hpp"
59 #include "MueLu_Exceptions.hpp"
60 #include "MueLu_LWGraph_kokkos.hpp"
61 #include "MueLu_Monitor.hpp"
62 
63 namespace MueLu {
64 
65  // Try to stick unaggregated nodes into a neighboring aggregate if they are
66  // not already too big. Otherwise, make a new aggregate
67  template <class LocalOrdinal, class GlobalOrdinal, class Node>
68  void AggregationPhase3Algorithm_kokkos<LocalOrdinal, GlobalOrdinal, Node>::BuildAggregates(const ParameterList& params, const LWGraph_kokkos& graph, Aggregates_kokkos& aggregates, std::vector<unsigned>& aggStat, LO& numNonAggregatedNodes) const {
69  Monitor m(*this, "BuildAggregates");
70 
71  bool error_on_isolated = false;
72  if(params.isParameter("aggregation: error on nodes with no on-rank neighbors"))
73  params.get<bool>("aggregation: error on nodes with no on-rank neighbors");
74 
75  const LO numRows = graph.GetNodeNumVertices();
76  const int myRank = graph.GetComm()->getRank();
77 
78  ArrayRCP<LO> vertex2AggId = aggregates.GetVertex2AggId()->getDataNonConst(0);
79  ArrayRCP<LO> procWinner = aggregates.GetProcWinner() ->getDataNonConst(0);
80 
81  LO numLocalAggregates = aggregates.GetNumAggregates();
82 
83  for (LO i = 0; i < numRows; i++) {
84  if (aggStat[i] == AGGREGATED || aggStat[i] == IGNORED)
85  continue;
86 
87  auto neighOfINode = graph.getNeighborVertices(i);
88 
89  // We don't want a singleton. So lets see if there is an unaggregated
90  // neighbor that we can also put with this point.
91  bool isNewAggregate = false;
92  for (int j = 0; j < as<int>(neighOfINode.length); j++) {
93  LO neigh = neighOfINode(j);
94 
95  if (neigh != i && graph.isLocalNeighborVertex(neigh) && aggStat[neigh] == READY) {
96  isNewAggregate = true;
97 
98  aggStat [neigh] = AGGREGATED;
99  vertex2AggId[neigh] = numLocalAggregates;
100  procWinner [neigh] = myRank;
101 
102  numNonAggregatedNodes--;
103  }
104  }
105 
106  if (isNewAggregate) {
107  // Create new aggregate (not singleton)
108  aggregates.SetIsRoot(i);
109  vertex2AggId[i] = numLocalAggregates++;
110 
111  } else {
112  // We do not want a singleton, but there are no non-aggregated
113  // neighbors. Lets see if we can connect to any other aggregates
114  // NOTE: This is very similar to phase 2b, but simpler: we stop with
115  // the first found aggregate
116  int j = 0;
117  for (; j < as<int>(neighOfINode.length); j++) {
118  LO neigh = neighOfINode(j);
119 
120  // We don't check (neigh != rootCandidate), as it is covered by checking (aggStat[neigh] == AGGREGATED)
121  if (graph.isLocalNeighborVertex(neigh) && aggStat[neigh] == AGGREGATED)
122  break;
123  }
124 
125  if (j < as<int>(neighOfINode.length)) {
126  // Assign to an adjacent aggregate
127  vertex2AggId[i] = vertex2AggId[neighOfINode(j)];
128  } else if (error_on_isolated) {
129  // Error on this isolated node, as the user has requested
130  std::ostringstream oss;
131  oss<<"MueLu::AggregationPhase3Algorithm::BuildAggregates: MueLu has detected a non-Dirichlet node that has no on-rank neighbors and is terminating (by user request). "<<std::endl;
132  oss<<"If this error is being generated at level 0, this is due to an initial partitioning problem in your matrix."<<std::endl;
133  oss<<"If this error is being generated at any other level, try turning on repartitioning, which may fix this problem."<<std::endl;
134  throw Exceptions::RuntimeError(oss.str());
135  } else {
136  // Create new aggregate (singleton)
137  this->GetOStream(Warnings1) << "Found singleton: " << i << std::endl;
138 
139  aggregates.SetIsRoot(i);
140  vertex2AggId[i] = numLocalAggregates++;
141  }
142  }
143 
144  // One way or another, the node is aggregated (possibly into a singleton)
145  aggStat [i] = AGGREGATED;
146  procWinner[i] = myRank;
147  numNonAggregatedNodes--;
148 
149  }
150 
151  // update aggregate object
152  aggregates.SetNumAggregates(numLocalAggregates);
153  }
154 
155 } // end namespace
156 
157 #endif // HAVE_MUELU_KOKKOS_REFACTOR
158 #endif // MUELU_AGGREGATIONPHASE3ALGORITHM_KOKKOS_DEF_HPP
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