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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  size_t numSingletons=0;
77 
78  const LO numRows = graph.GetNodeNumVertices();
79  const int myRank = graph.GetComm()->getRank();
80 
81  ArrayRCP<LO> vertex2AggId = aggregates.GetVertex2AggId()->getDataNonConst(0);
82  ArrayRCP<LO> procWinner = aggregates.GetProcWinner() ->getDataNonConst(0);
83 
84  LO numLocalAggregates = aggregates.GetNumAggregates();
85 
86  for (LO i = 0; i < numRows; i++) {
87  if (aggStat[i] == AGGREGATED || aggStat[i] == IGNORED)
88  continue;
89 
90  ArrayView<const LocalOrdinal> neighOfINode = graph.getNeighborVertices(i);
91 
92  // We don't want a singleton. So lets see if there is an unaggregated
93  // neighbor that we can also put with this point.
94  bool isNewAggregate = false;
95  bool failedToAggregate = true;
96  for (int j = 0; j < neighOfINode.size(); j++) {
97  LO neigh = neighOfINode[j];
98 
99  if (neigh != i && graph.isLocalNeighborVertex(neigh) && aggStat[neigh] == READY) {
100  isNewAggregate = true;
101 
102  aggStat [neigh] = AGGREGATED;
103  vertex2AggId[neigh] = numLocalAggregates;
104  procWinner [neigh] = myRank;
105 
106  numNonAggregatedNodes--;
107  }
108  }
109 
110  if (isNewAggregate) {
111  // Create new aggregate (not singleton)
112  aggStat [i] = AGGREGATED;
113  procWinner [i] = myRank;
114  numNonAggregatedNodes--;
115  aggregates.SetIsRoot(i);
116  vertex2AggId[i] = numLocalAggregates++;
117 
118  failedToAggregate = false;
119  } else {
120  // We do not want a singleton, but there are no non-aggregated
121  // neighbors. Lets see if we can connect to any other aggregates
122  // NOTE: This is very similar to phase 2b, but simplier: we stop with
123  // the first found aggregate
124  int j = 0;
125  for (; j < neighOfINode.size(); j++) {
126  LO neigh = neighOfINode[j];
127 
128  // We don't check (neigh != rootCandidate), as it is covered by checking (aggStat[neigh] == AGGREGATED)
129  if (graph.isLocalNeighborVertex(neigh) && aggStat[neigh] == AGGREGATED)
130  break;
131  }
132 
133  if (j < neighOfINode.size()) {
134  // Assign to an adjacent aggregate
135  vertex2AggId[i] = vertex2AggId[neighOfINode[j]];
136  numNonAggregatedNodes--;
137  failedToAggregate = false;
138  }
139  }
140 
141  if (failedToAggregate && makeNonAdjAggs) {
142  // it we are still didn't find an aggregate home for i (i.e., we have
143  // a potential singleton), we are desperate. Basically, we seek to
144  // group i with any other local point to form an aggregate (even if
145  // it is not a neighbor of i. Either we find a vertex that is already
146  // aggregated or not aggregated.
147  // 1) if found vertex is aggregated, then assign i to this aggregate
148  // 2) if found vertex is not aggregated, create new aggregate
149 
150 
151  for (LO ii = 0; ii < numRows; ii++) { // look for anyone else
152  if ( (ii != i) && (aggStat[ii] != IGNORED) ) {
153  failedToAggregate = false; // found someone so start
154  aggStat[i] = AGGREGATED; // marking i as aggregated
155  procWinner[i]= myRank;
156 
157  if (aggStat[ii] == AGGREGATED)
158  vertex2AggId[i] = vertex2AggId[ii];
159  else {
160  vertex2AggId[i] = numLocalAggregates;
161  vertex2AggId[ii] = numLocalAggregates;
162  aggStat [ii] = AGGREGATED;
163  procWinner [ii] = myRank;
164  numNonAggregatedNodes--; // acounts for ii now being aggregated
165  aggregates.SetIsRoot(i);
166  numLocalAggregates++;
167  }
168  numNonAggregatedNodes--; // accounts for i now being aggregated
169  break;
170  } //if ( (ii != i) && (aggStat[ii] != IGNORED ...
171  } //for (LO ii = 0; ...
172  }
173  if (failedToAggregate) {
174  if (error_on_isolated) {
175  // Error on this isolated node, as the user has requested
176  std::ostringstream oss;
177  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;
178  oss<<"If this error is being generated at level 0, this is due to an initial partitioning problem in your matrix."<<std::endl;
179  oss<<"If this error is being generated at any other level, try turning on repartitioning, which may fix this problem."<<std::endl;
180  throw Exceptions::RuntimeError(oss.str());
181  } else {
182  // Create new aggregate (singleton)
183  // this->GetOStream(Warnings1) << "Found singleton: " << i << std::endl;
184  numSingletons++;
185 
186  aggregates.SetIsRoot(i);
187  vertex2AggId[i] = numLocalAggregates++;
188  numNonAggregatedNodes--;
189  }
190  }
191 
192  // One way or another, the node is aggregated (possibly into a singleton)
193  aggStat [i] = AGGREGATED;
194  procWinner[i] = myRank;
195 
196  } // loop over numRows
197 
198 
199  if(numSingletons > 0)
200  this->GetOStream(Runtime0)<<" WARNING Rank "<<myRank<<" singletons :"<<numSingletons<<" (phase)"<<std::endl;
201 
202 
203  // update aggregate object
204  aggregates.SetNumAggregates(numLocalAggregates);
205  }
206 
207 } // end namespace
208 
209 #endif /* MUELU_AGGREGATIONPHASE3ALGORITHM_DEF_HPP_ */
Container class for aggregation information.
void BuildAggregates(const ParameterList &params, const GraphBase &graph, Aggregates &aggregates, std::vector< unsigned > &aggStat, LO &numNonAggregatedNodes) const
Local aggregation.
virtual size_t GetNodeNumVertices() const =0
Return number of vertices owned by the calling node.
One-liner description of what is happening.
Namespace for MueLu classes and methods.
void SetIsRoot(LO i, bool value=true)
Set root node information.
virtual bool isLocalNeighborVertex(LocalOrdinal v) const =0
Return true if vertex with local id &#39;v&#39; is on current process.
virtual const RCP< const Teuchos::Comm< int > > GetComm() const =0
MueLu representation of a graph.
Timer to be used in non-factories.
LO GetNumAggregates() const
returns the number of aggregates of the current processor. Note: could/should be renamed to GetNumLoc...
const RCP< LOMultiVector > & GetVertex2AggId() const
Returns constant vector that maps local node IDs to local aggregates IDs.
Exception throws to report errors in the internal logical of the program.
const RCP< LOVector > & GetProcWinner() const
Returns constant vector that maps local node IDs to owning processor IDs.
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.