org.jgrapht.alg.matching.blossom.v5

Class KolmogorovMinimumWeightPerfectMatching<V,E>

• java.lang.Object
• org.jgrapht.alg.matching.blossom.v5.KolmogorovMinimumWeightPerfectMatching<V,E>
• Type Parameters:
V - the graph vertex type
E - the graph edge type
All Implemented Interfaces:
MatchingAlgorithm<V,E>

public class KolmogorovMinimumWeightPerfectMatching<V,E>
extends Object
implements MatchingAlgorithm<V,E>
This class computes a minimum weight perfect matching in general graphs using the Blossom V algorithm.

Let $G = (V, E, c)$ be an undirected graph with a real-valued cost function defined on it. A matching is an edge-disjoint subset of edges $M \subseteq E$. A matching is perfect if $2|M| = |V|$. In the minimum weight perfect matching problem the goal is to minimize the weighted sum of the edges in the perfect matching. This class supports pseudographs, but a problem on a pseudograph can be easily reduced to a problem on a simple graph. Moreover, this reduction can heavily influence the running time since only an edge with minimum weight between two vertices can belong to the matching. Currently, users are responsible for doing this reduction themselves before invoking the algorithm.

Note that if the graph is unweighted and dense, EdmondsMaximumCardinalityMatching may be a better choice.

For more information about the algorithm see the following paper: Kolmogorov, V. Math. Prog. Comp. (2009) 1: 43. https://doi.org/10.1007/s12532-009-0002-8, and the original implementation: http://pub.ist.ac.at/~vnk/software/blossom5-v2.05.src.tar.gz

The algorithm can be divided into two phases: initialization and the main algorithm. The initialization phase is responsible for converting the specified graph into the form convenient for the algorithm and for finding an initial matching to speed up the main part. Furthermore, the main part of the algorithm can be further divided into primal and dual updates. The primal phases are aimed at augmenting the matching so that the value of the objective function of the primal linear program increases. Dual updates are aimed at increasing the objective function of the dual linear program. The algorithm iteratively performs these primal and dual operations to build alternating trees of tight edges and augment the matching. Thus, at any stage of the algorithm the matching consists of tight edges. This means that the resulting perfect matching meets complementary slackness conditions, and is therefore optimal.

At construction time the set of options can be specified to define the strategies used by the algorithm to perform initialization, dual updates, etc. This can be done with the BlossomVOptions. This class supports retrieving statistics for the algorithm performance; see getStatistics(). It provides the time elapsed during primal operations and dual updates, as well as the number of these primal operations performed.

The solution to a minimum weight perfect matching problem instance comes with a certificate of optimality, which is represented by a solution to a dual linear program; see KolmogorovMinimumWeightPerfectMatching.DualSolution. This class encapsulates a mapping from the node sets of odd cardinality to the corresponding dual variables. This mapping doesn't contain the sets whose dual variables are $0$. The computation of the dual solution is performed lazily and doesn't affect the running time of finding a minimum weight perfect matching.

This class supports testing the optimality of the solution via testOptimality(). It also supports retrieval of the computation error when the edge weights are real values via getError(). Both optimality test and error computation are performed lazily and don't affect the running time of the main algorithm. If the problem instance doesn't contain a perfect matching at all, the algorithm doesn't find a minimum weight maximum matching; instead, it throws an exception.

Author:
Timofey Chudakov
BlossomVPrimalUpdater, BlossomVDualUpdater
• Nested Class Summary

Nested Classes
Modifier and Type Class and Description
static class  KolmogorovMinimumWeightPerfectMatching.DualSolution<V,E>
A solution to the dual linear program formulated on the graph
static class  KolmogorovMinimumWeightPerfectMatching.Statistics
Describes the performance characteristics of the algorithm and numeric data about the number of performed dual operations during the main phase of the algorithm
• Nested classes/interfaces inherited from interface org.jgrapht.alg.interfaces.MatchingAlgorithm

MatchingAlgorithm.Matching<V,E>, MatchingAlgorithm.MatchingImpl<V,E>
• Field Summary

Fields
Modifier and Type Field and Description
static double EPS
Default epsilon used in the algorithm
static double INFINITY
Default infinity value used in the algorithm
static double NO_PERFECT_MATCHING_THRESHOLD
Defines the threshold for throwing an exception about no perfect matching existence
• Fields inherited from interface org.jgrapht.alg.interfaces.MatchingAlgorithm

DEFAULT_EPSILON
• Constructor Summary

Constructors
Constructor and Description
KolmogorovMinimumWeightPerfectMatching(Graph<V,E> graph)
Constructs a new instance of the algorithm using the default options.
KolmogorovMinimumWeightPerfectMatching(Graph<V,E> graph, BlossomVOptions options)
Constructs a new instance of the algorithm with the specified options
• Method Summary

All Methods
Modifier and Type Method and Description
KolmogorovMinimumWeightPerfectMatching.DualSolution<V,E> getDualSolution()
Returns the computed solution to the dual linear program with respect to the minimum weight perfect matching linear program formulation.
double getError()
Computes the error in the solution to the dual linear program.
MatchingAlgorithm.Matching<V,E> getMatching()
Computes and returns a minimum weight perfect matching in the graph.
KolmogorovMinimumWeightPerfectMatching.Statistics getStatistics()
Returns the statistics describing the performance characteristics of the algorithm.
boolean testOptimality()
Performs an optimality test after the perfect matching is computed.
• Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
• Field Detail

• EPS

public static final double EPS
Default epsilon used in the algorithm
Constant Field Values
• INFINITY

public static final double INFINITY
Default infinity value used in the algorithm
Constant Field Values
• NO_PERFECT_MATCHING_THRESHOLD

public static final double NO_PERFECT_MATCHING_THRESHOLD
Defines the threshold for throwing an exception about no perfect matching existence
Constant Field Values
• Constructor Detail

• KolmogorovMinimumWeightPerfectMatching

public KolmogorovMinimumWeightPerfectMatching(Graph<V,E> graph)
Constructs a new instance of the algorithm using the default options.
Parameters:
graph - the graph for which to find a minimum weight perfect matching
• KolmogorovMinimumWeightPerfectMatching

public KolmogorovMinimumWeightPerfectMatching(Graph<V,E> graph,
BlossomVOptions options)
Constructs a new instance of the algorithm with the specified options
Parameters:
graph - the graph for which to find a minimum weight perfect matching
options - the options which define the strategies for the initialization and dual updates
• Method Detail

• getMatching

public MatchingAlgorithm.Matching<V,E> getMatching()
Computes and returns a minimum weight perfect matching in the graph. See the class description for the relative definitions and algorithm description.
Specified by:
getMatching in interface MatchingAlgorithm<V,E>
Returns:
the minimum weight perfect matching for the graph
• getDualSolution

public KolmogorovMinimumWeightPerfectMatching.DualSolution<V,E> getDualSolution()
Returns the computed solution to the dual linear program with respect to the minimum weight perfect matching linear program formulation.
Returns:
the solution to the dual linear program formulated on the graph
• testOptimality

public boolean testOptimality()
Performs an optimality test after the perfect matching is computed.

More precisely, checks whether dual variables of all pseudonodes and resulting slacks of all edges are non-negative and that slacks of all matched edges are exactly 0. Since the algorithm uses floating point arithmetic, this check is done with precision of EPS

In general, this method should always return true unless the algorithm implementation has a bug.

Returns:
true iff the assigned dual variables satisfy the dual linear program formulation AND complementary slackness conditions are also satisfied. The total error must not exceed EPS
• getError

public double getError()
Computes the error in the solution to the dual linear program. More precisely, the total error equals the sum of:
• Absolute value of edge slack if negative or the edge is matched
• Absolute value of pseudonode variable if negative
Returns:
the total numeric error
• getStatistics

public KolmogorovMinimumWeightPerfectMatching.Statistics getStatistics()
Returns the statistics describing the performance characteristics of the algorithm.
Returns:
the statistics describing the algorithms characteristics