1 // Ceres Solver - A fast non-linear least squares minimizer
2 // Copyright 2015 Google Inc. All rights reserved.
3 // http://ceres-solver.org/
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29 // Author: sameeragarwal@google.com (Sameer Agarwal)
31 #include "ceres/single_linkage_clustering.h"
33 #include "ceres/graph.h"
34 #include "ceres/collections_port.h"
35 #include "ceres/graph_algorithms.h"
40 int ComputeSingleLinkageClustering(
41 const SingleLinkageClusteringOptions& options,
42 const WeightedGraph<int>& graph,
43 HashMap<int, int>* membership) {
44 CHECK_NOTNULL(membership)->clear();
46 // Initially each vertex is in its own cluster.
47 const HashSet<int>& vertices = graph.vertices();
48 for (HashSet<int>::const_iterator it = vertices.begin();
51 (*membership)[*it] = *it;
54 for (HashSet<int>::const_iterator it1 = vertices.begin();
55 it1 != vertices.end();
57 const int vertex1 = *it1;
58 const HashSet<int>& neighbors = graph.Neighbors(vertex1);
59 for (HashSet<int>::const_iterator it2 = neighbors.begin();
60 it2 != neighbors.end();
62 const int vertex2 = *it2;
64 // Since the graph is undirected, only pay attention to one side
65 // of the edge and ignore weak edges.
66 if ((vertex1 > vertex2) ||
67 (graph.EdgeWeight(vertex1, vertex2) < options.min_similarity)) {
71 // Use a union-find algorithm to keep track of the clusters.
72 const int c1 = FindConnectedComponent(vertex1, membership);
73 const int c2 = FindConnectedComponent(vertex2, membership);
80 (*membership)[c2] = c1;
82 (*membership)[c1] = c2;
87 // Make sure that every vertex is connected directly to the vertex
88 // identifying the cluster.
90 for (HashMap<int, int>::iterator it = membership->begin();
91 it != membership->end();
93 it->second = FindConnectedComponent(it->first, membership);
94 if (it->first == it->second) {
102 } // namespace internal