| // Ceres Solver - A fast non-linear least squares minimizer |
| // Copyright 2023 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 "absl/container/flat_hash_map.h" |
| #include "absl/container/flat_hash_set.h" |
| #include "absl/log/check.h" |
| #include "ceres/graph.h" |
| #include "ceres/graph_algorithms.h" |
| |
| namespace ceres::internal { |
| |
| int ComputeSingleLinkageClustering( |
| const SingleLinkageClusteringOptions& options, |
| const WeightedGraph<int>& graph, |
| absl::flat_hash_map<int, int>* membership) { |
| CHECK(membership != nullptr); |
| membership->clear(); |
| |
| // Initially each vertex is in its own cluster. |
| const absl::flat_hash_set<int>& vertices = graph.vertices(); |
| for (const int v : vertices) { |
| (*membership)[v] = v; |
| } |
| |
| for (const int vertex1 : vertices) { |
| const absl::flat_hash_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 ceres::internal |