internal/ceres/graph.h

// Ceres Solver - A fast non-linear least squares minimizer
// Copyright 2010, 2011, 2012 Google Inc. All rights reserved.
// http://code.google.com/p/ceres-solver/
//
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// modification, are permitted provided that the following conditions are met:
//
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//   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.
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//   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
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// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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// Author: sameeragarwal@google.com (Sameer Agarwal)

#ifndef CERES_INTERNAL_GRAPH_H_
#define CERES_INTERNAL_GRAPH_H_

#include <limits>
#include <glog/logging.h>
#include "ceres/integral_types.h"
#include "ceres/map_util.h"
#include "ceres/collections_port.h"
#include "ceres/internal/macros.h"
#include "ceres/types.h"

namespace ceres {
namespace internal {

// A weighted undirected graph templated over the vertex ids. Vertex
// should be hashable and comparable.
template <typename Vertex>
class Graph {
 public:
  Graph() {}

  // Add a weighted vertex. If the vertex already exists in the graph,
  // its weight is set to the new weight.
  void AddVertex(const Vertex& vertex, double weight) {
    if (vertices_.find(vertex) == vertices_.end()) {
      vertices_.insert(vertex);
      edges_[vertex] = HashSet<Vertex>();
    }
    vertex_weights_[vertex] = weight;
  }

  // Uses weight = 1.0. If vertex already exists, its weight is set to
  // 1.0.
  void AddVertex(const Vertex& vertex) {
    AddVertex(vertex, 1.0);
  }

  // Add a weighted edge between the vertex1 and vertex2. Calling
  // AddEdge on a pair of vertices which do not exist in the graph yet
  // will result in undefined behavior.
  //
  // It is legal to call this method repeatedly for the same set of
  // vertices.
  void AddEdge(const Vertex& vertex1, const Vertex& vertex2, double weight) {
    DCHECK(vertices_.find(vertex1) != vertices_.end());
    DCHECK(vertices_.find(vertex2) != vertices_.end());

    if (edges_[vertex1].insert(vertex2).second) {
      edges_[vertex2].insert(vertex1);
    }

    if (vertex1 < vertex2) {
      edge_weights_[make_pair(vertex1, vertex2)] = weight;
    } else {
      edge_weights_[make_pair(vertex2, vertex1)] = weight;
    }
  }

  // Uses weight = 1.0.
  void AddEdge(const Vertex& vertex1, const Vertex& vertex2) {
    AddEdge(vertex1, vertex2, 1.0);
  }

  // Calling VertexWeight on a vertex not in the graph will result in
  // undefined behavior.
  double VertexWeight(const Vertex& vertex) const {
    return FindOrDie(vertex_weights_, vertex);
  }

  // Calling EdgeWeight on a pair of vertices where either one of the
  // vertices is not present in the graph will result in undefined
  // behaviour. If there is no edge connecting vertex1 and vertex2,
  // the edge weight is zero.
  double EdgeWeight(const Vertex& vertex1, const Vertex& vertex2) const {
    if (vertex1 < vertex2) {
      return FindWithDefault(edge_weights_, make_pair(vertex1, vertex2), 0.0);
    } else {
      return FindWithDefault(edge_weights_, make_pair(vertex2, vertex1), 0.0);
    }
  }

  // Calling Neighbors on a vertex not in the graph will result in
  // undefined behaviour.
  const HashSet<Vertex>& Neighbors(const Vertex& vertex) const {
    return FindOrDie(edges_, vertex);
  }

  const HashSet<Vertex>& vertices() const {
    return vertices_;
  }

  static double InvalidWeight() {
    return std::numeric_limits<double>::quiet_NaN();
  };

 private:
  HashSet<Vertex> vertices_;
  HashMap<Vertex, double> vertex_weights_;
  HashMap<Vertex, HashSet<Vertex> > edges_;
  HashMap<pair<Vertex, Vertex>, double> edge_weights_;

  CERES_DISALLOW_COPY_AND_ASSIGN(Graph);
};

}  // namespace internal
}  // namespace ceres

#endif  // CERES_INTERNAL_GRAPH_H_