Squashed 'third_party/ceres/' content from commit e51e9b4
Change-Id: I763587619d57e594d3fa158dc3a7fe0b89a1743b
git-subtree-dir: third_party/ceres
git-subtree-split: e51e9b46f6ca88ab8b2266d0e362771db6d98067
diff --git a/internal/ceres/single_linkage_clustering.cc b/internal/ceres/single_linkage_clustering.cc
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+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 2015 Google Inc. All rights reserved.
+// http://ceres-solver.org/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// * Redistributions of source code must retain the above copyright notice,
+// this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above copyright notice,
+// this list of conditions and the following disclaimer in the documentation
+// and/or other materials provided with the distribution.
+// * Neither the name of Google Inc. nor the names of its contributors may be
+// used to endorse or promote products derived from this software without
+// specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+// Author: sameeragarwal@google.com (Sameer Agarwal)
+
+#include "ceres/single_linkage_clustering.h"
+
+#include <unordered_set>
+#include <unordered_map>
+#include "ceres/graph.h"
+#include "ceres/graph_algorithms.h"
+
+namespace ceres {
+namespace internal {
+
+int ComputeSingleLinkageClustering(
+ const SingleLinkageClusteringOptions& options,
+ const WeightedGraph<int>& graph,
+ std::unordered_map<int, int>* membership) {
+ CHECK(membership != nullptr);
+ membership->clear();
+
+ // Initially each vertex is in its own cluster.
+ const std::unordered_set<int>& vertices = graph.vertices();
+ for (const int v : vertices) {
+ (*membership)[v] = v;
+ }
+
+ for (const int vertex1 : vertices) {
+ const std::unordered_set<int>& neighbors = graph.Neighbors(vertex1);
+ for (const int vertex2 : neighbors) {
+ // Since the graph is undirected, only pay attention to one side
+ // of the edge and ignore weak edges.
+ if ((vertex1 > vertex2) ||
+ (graph.EdgeWeight(vertex1, vertex2) < options.min_similarity)) {
+ continue;
+ }
+
+ // Use a union-find algorithm to keep track of the clusters.
+ const int c1 = FindConnectedComponent(vertex1, membership);
+ const int c2 = FindConnectedComponent(vertex2, membership);
+
+ if (c1 == c2) {
+ continue;
+ }
+
+ if (c1 < c2) {
+ (*membership)[c2] = c1;
+ } else {
+ (*membership)[c1] = c2;
+ }
+ }
+ }
+
+ // Make sure that every vertex is connected directly to the vertex
+ // identifying the cluster.
+ int num_clusters = 0;
+ for (auto& m : *membership) {
+ m.second = FindConnectedComponent(m.first, membership);
+ if (m.first == m.second) {
+ ++num_clusters;
+ }
+ }
+
+ return num_clusters;
+}
+
+} // namespace internal
+} // namespace ceres