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MueLu_AggregationPhase3Algorithm_def.hpp
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46 #ifndef MUELU_AGGREGATIONPHASE3ALGORITHM_DEF_HPP_
47 #define MUELU_AGGREGATIONPHASE3ALGORITHM_DEF_HPP_
48 
49 #include <Teuchos_Comm.hpp>
50 #include <Teuchos_CommHelpers.hpp>
51 
52 #include <Xpetra_Vector.hpp>
53 
55 
56 #include "MueLu_Aggregates.hpp"
57 #include "MueLu_Exceptions.hpp"
58 #include "MueLu_GraphBase.hpp"
59 #include "MueLu_Monitor.hpp"
60 
61 namespace MueLu {
62 
63  // Try to stick unaggregated nodes into a neighboring aggregate if they are
64  // not already too big. Otherwise, make a new aggregate
65  template <class LocalOrdinal, class GlobalOrdinal, class Node>
66  void AggregationPhase3Algorithm<LocalOrdinal, GlobalOrdinal, Node>::BuildAggregates(const ParameterList& params, const GraphBase& graph, Aggregates& aggregates, std::vector<unsigned>& aggStat, LO& numNonAggregatedNodes) const {
67  Monitor m(*this, "BuildAggregates");
68 
69  bool makeNonAdjAggs = false;
70  bool error_on_isolated = false;
71  if(params.isParameter("aggregation: error on nodes with no on-rank neighbors"))
72  error_on_isolated = params.get<bool>("aggregation: error on nodes with no on-rank neighbors");
73  if(params.isParameter("aggregation: phase3 avoid singletons"))
74  makeNonAdjAggs = params.get<bool>("aggregation: phase3 avoid singletons");
75 
76  const LO numRows = graph.GetNodeNumVertices();
77  const int myRank = graph.GetComm()->getRank();
78 
79  ArrayRCP<LO> vertex2AggId = aggregates.GetVertex2AggId()->getDataNonConst(0);
80  ArrayRCP<LO> procWinner = aggregates.GetProcWinner() ->getDataNonConst(0);
81 
82  LO numLocalAggregates = aggregates.GetNumAggregates();
83 
84  for (LO i = 0; i < numRows; i++) {
85  if (aggStat[i] == AGGREGATED || aggStat[i] == IGNORED)
86  continue;
87 
88  ArrayView<const LocalOrdinal> neighOfINode = graph.getNeighborVertices(i);
89 
90  // We don't want a singleton. So lets see if there is an unaggregated
91  // neighbor that we can also put with this point.
92  bool isNewAggregate = false;
93  bool failedToAggregate = true;
94  for (int j = 0; j < neighOfINode.size(); j++) {
95  LO neigh = neighOfINode[j];
96 
97  if (neigh != i && graph.isLocalNeighborVertex(neigh) && aggStat[neigh] == READY) {
98  isNewAggregate = true;
99 
100  aggStat [neigh] = AGGREGATED;
101  vertex2AggId[neigh] = numLocalAggregates;
102  procWinner [neigh] = myRank;
103 
104  numNonAggregatedNodes--;
105  }
106  }
107 
108  if (isNewAggregate) {
109  // Create new aggregate (not singleton)
110  aggStat [i] = AGGREGATED;
111  procWinner [i] = myRank;
112  numNonAggregatedNodes--;
113  aggregates.SetIsRoot(i);
114  vertex2AggId[i] = numLocalAggregates++;
115 
116  failedToAggregate = false;
117  } else {
118  // We do not want a singleton, but there are no non-aggregated
119  // neighbors. Lets see if we can connect to any other aggregates
120  // NOTE: This is very similar to phase 2b, but simplier: we stop with
121  // the first found aggregate
122  int j = 0;
123  for (; j < neighOfINode.size(); j++) {
124  LO neigh = neighOfINode[j];
125 
126  // We don't check (neigh != rootCandidate), as it is covered by checking (aggStat[neigh] == AGGREGATED)
127  if (graph.isLocalNeighborVertex(neigh) && aggStat[neigh] == AGGREGATED)
128  break;
129  }
130 
131  if (j < neighOfINode.size()) {
132  // Assign to an adjacent aggregate
133  vertex2AggId[i] = vertex2AggId[neighOfINode[j]];
134  numNonAggregatedNodes--;
135  failedToAggregate = false;
136  }
137  }
138 
139  if (failedToAggregate && makeNonAdjAggs) {
140  // it we are still didn't find an aggregate home for i (i.e., we have
141  // a potential singleton), we are desperate. Basically, we seek to
142  // group i with any other local point to form an aggregate (even if
143  // it is not a neighbor of i. Either we find a vertex that is already
144  // aggregated or not aggregated.
145  // 1) if found vertex is aggregated, then assign i to this aggregate
146  // 2) if found vertex is not aggregated, create new aggregate
147 
148 
149  for (LO ii = 0; ii < numRows; ii++) { // look for anyone else
150  if ( (ii != i) && (aggStat[ii] != IGNORED) ) {
151  failedToAggregate = false; // found someone so start
152  aggStat[i] = AGGREGATED; // marking i as aggregated
153  procWinner[i]= myRank;
154 
155  if (aggStat[ii] == AGGREGATED)
156  vertex2AggId[i] = vertex2AggId[ii];
157  else {
158  vertex2AggId[i] = numLocalAggregates;
159  vertex2AggId[ii] = numLocalAggregates;
160  aggStat [ii] = AGGREGATED;
161  procWinner [ii] = myRank;
162  numNonAggregatedNodes--; // acounts for ii now being aggregated
163  aggregates.SetIsRoot(i);
164  numLocalAggregates++;
165  }
166  numNonAggregatedNodes--; // accounts for i now being aggregated
167  break;
168  } //if ( (ii != i) && (aggStat[ii] != IGNORED ...
169  } //for (LO ii = 0; ...
170  }
171  if (failedToAggregate) {
172  if (error_on_isolated) {
173  // Error on this isolated node, as the user has requested
174  std::ostringstream oss;
175  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;
176  oss<<"If this error is being generated at level 0, this is due to an initial partitioning problem in your matrix."<<std::endl;
177  oss<<"If this error is being generated at any other level, try turning on repartitioning, which may fix this problem."<<std::endl;
178  throw Exceptions::RuntimeError(oss.str());
179  } else {
180  // Create new aggregate (singleton)
181  this->GetOStream(Warnings1) << "Found singleton: " << i << std::endl;
182 
183  aggregates.SetIsRoot(i);
184  vertex2AggId[i] = numLocalAggregates++;
185  numNonAggregatedNodes--;
186  }
187  }
188 
189  // One way or another, the node is aggregated (possibly into a singleton)
190  aggStat [i] = AGGREGATED;
191  procWinner[i] = myRank;
192 
193  }
194 
195  // update aggregate object
196  aggregates.SetNumAggregates(numLocalAggregates);
197  }
198 
199 } // end namespace
200 
201 #endif /* MUELU_AGGREGATIONPHASE3ALGORITHM_DEF_HPP_ */
const RCP< LOVector > & GetProcWinner() const
Returns constant vector that maps local node IDs to owning processor IDs.
Container class for aggregation information.
T & get(const std::string &name, T def_value)
virtual size_t GetNodeNumVertices() const =0
Return number of vertices owned by the calling node.
size_type size() const
LocalOrdinal LO
void SetIsRoot(LO i, bool value=true)
Set root node information.
Additional warnings.
bool isParameter(const std::string &name) const
void BuildAggregates(const ParameterList &params, const GraphBase &graph, Aggregates &aggregates, std::vector< unsigned > &aggStat, LO &numNonAggregatedNodes) const
Local aggregation.
LO GetNumAggregates() const
returns the number of aggregates of the current processor. Note: could/should be renamed to GetNumLoc...
virtual bool isLocalNeighborVertex(LocalOrdinal v) const =0
Return true if vertex with local id &#39;v&#39; is on current process.
const RCP< LOMultiVector > & GetVertex2AggId() const
Returns constant vector that maps local node IDs to local aggregates IDs.
virtual const RCP< const Teuchos::Comm< int > > GetComm() const =0
MueLu representation of a graph.
Timer to be used in non-factories.
Exception throws to report errors in the internal logical of the program.
virtual Teuchos::ArrayView< const LocalOrdinal > getNeighborVertices(LocalOrdinal v) const =0
Return the list of vertices adjacent to the vertex &#39;v&#39;.
void SetNumAggregates(LO nAggregates)
Set number of local aggregates on current processor.