1 // Ceres Solver - A fast non-linear least squares minimizer
2 // Copyright 2013 Google Inc. All rights reserved.
3 // http://code.google.com/p/ceres-solver/
4 //
5 // Redistribution and use in source and binary forms, with or without
6 // modification, are permitted provided that the following conditions are met:
7 //
8 // * Redistributions of source code must retain the above copyright notice,
9 // this list of conditions and the following disclaimer.
10 // * Redistributions in binary form must reproduce the above copyright notice,
11 // this list of conditions and the following disclaimer in the documentation
12 // and/or other materials provided with the distribution.
13 // * Neither the name of Google Inc. nor the names of its contributors may be
14 // used to endorse or promote products derived from this software without
15 // specific prior written permission.
16 //
17 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
18 // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 // ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
21 // LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
22 // CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
23 // SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
24 // INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
25 // CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
26 // ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
27 // POSSIBILITY OF SUCH DAMAGE.
28 //
29 // Author: sameeragarwal@google.com (Sameer Agarwal)
30
31 // This include must come before any #ifndef check on Ceres compile options.
32 #include "ceres/internal/port.h"
33
34 #ifndef CERES_NO_SUITESPARSE
35
36 #include "ceres/single_linkage_clustering.h"
37
38 #include "ceres/graph.h"
39 #include "ceres/collections_port.h"
40 #include "ceres/graph_algorithms.h"
41
42 namespace ceres {
43 namespace internal {
44
ComputeSingleLinkageClustering(const SingleLinkageClusteringOptions & options,const Graph<int> & graph,HashMap<int,int> * membership)45 int ComputeSingleLinkageClustering(
46 const SingleLinkageClusteringOptions& options,
47 const Graph<int>& graph,
48 HashMap<int, int>* membership) {
49 CHECK_NOTNULL(membership)->clear();
50
51 // Initially each vertex is in its own cluster.
52 const HashSet<int>& vertices = graph.vertices();
53 for (HashSet<int>::const_iterator it = vertices.begin();
54 it != vertices.end();
55 ++it) {
56 (*membership)[*it] = *it;
57 }
58
59 for (HashSet<int>::const_iterator it1 = vertices.begin();
60 it1 != vertices.end();
61 ++it1) {
62 const int vertex1 = *it1;
63 const HashSet<int>& neighbors = graph.Neighbors(vertex1);
64 for (HashSet<int>::const_iterator it2 = neighbors.begin();
65 it2 != neighbors.end();
66 ++it2) {
67 const int vertex2 = *it2;
68
69 // Since the graph is undirected, only pay attention to one side
70 // of the edge and ignore weak edges.
71 if ((vertex1 > vertex2) ||
72 (graph.EdgeWeight(vertex1, vertex2) < options.min_similarity)) {
73 continue;
74 }
75
76 // Use a union-find algorithm to keep track of the clusters.
77 const int c1 = FindConnectedComponent(vertex1, membership);
78 const int c2 = FindConnectedComponent(vertex2, membership);
79
80 if (c1 == c2) {
81 continue;
82 }
83
84 if (c1 < c2) {
85 (*membership)[c2] = c1;
86 } else {
87 (*membership)[c1] = c2;
88 }
89 }
90 }
91
92 // Make sure that every vertex is connected directly to the vertex
93 // identifying the cluster.
94 int num_clusters = 0;
95 for (HashMap<int, int>::iterator it = membership->begin();
96 it != membership->end();
97 ++it) {
98 it->second = FindConnectedComponent(it->first, membership);
99 if (it->first == it->second) {
100 ++num_clusters;
101 }
102 }
103
104 return num_clusters;
105 }
106
107 } // namespace internal
108 } // namespace ceres
109
110 #endif // CERES_NO_SUITESPARSE
111