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
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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
42namespace ceres {
43namespace internal {
44
45int 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