Class EdmondsKarpMaximumFlow<V,​E>


  • public final class EdmondsKarpMaximumFlow<V,​E>
    extends java.lang.Object
    A flow network is a directed graph where each edge has a capacity and each edge receives a flow. The amount of flow on an edge can not exceed the capacity of the edge (note, that all capacities must be non-negative). A flow must satisfy the restriction that the amount of flow into a vertex equals the amount of flow out of it, except when it is a source, which "produces" flow, or sink, which "consumes" flow.

    This class computes maximum flow in a network using Edmonds-Karp algorithm. Be careful: for large networks this algorithm may consume significant amount of time (its upper-bound complexity is O(VE^2), where V - amount of vertices, E - amount of edges in the network).

    For more details see Andrew V. Goldberg's Combinatorial Optimization (Lecture Notes).

    • Field Summary

      Fields 
      Modifier and Type Field Description
      static double DEFAULT_EPSILON
      Default tolerance.
    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void calculateMaximumFlow​(V source, V sink)
      Sets current source to source, current sink to sink, then calculates maximum flow from source to sink.
      V getCurrentSink()
      Returns current sink vertex, or null if there was no calculateMaximumFlow calls.
      V getCurrentSource()
      Returns current source vertex, or null if there was no calculateMaximumFlow calls.
      java.util.Map<E,​java.lang.Double> getMaximumFlow()
      Returns maximum flow, that was calculated during last calculateMaximumFlow call, or null, if there was no calculateMaximumFlow calls.
      java.lang.Double getMaximumFlowValue()
      Returns maximum flow value, that was calculated during last calculateMaximumFlow call, or null, if there was no calculateMaximumFlow calls.
      • Methods inherited from class java.lang.Object

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

      • DEFAULT_EPSILON

        public static final double DEFAULT_EPSILON
        Default tolerance.
        See Also:
        Constant Field Values
    • Constructor Detail

      • EdmondsKarpMaximumFlow

        public EdmondsKarpMaximumFlow​(DirectedGraph<V,​E> network)
        Constructs MaximumFlow instance to work with a copy of network. Current source and sink are set to null. If network is weighted, then capacities are weights, otherwise all capacities are equal to one. Doubles are compared using DEFAULT_EPSILON tolerance.
        Parameters:
        network - network, where maximum flow will be calculated
      • EdmondsKarpMaximumFlow

        public EdmondsKarpMaximumFlow​(DirectedGraph<V,​E> network,
                                      double epsilon)
        Constructs MaximumFlow instance to work with a copy of network. Current source and sink are set to null. If network is weighted, then capacities are weights, otherwise all capacities are equal to one.
        Parameters:
        network - network, where maximum flow will be calculated
        epsilon - tolerance for comparing doubles
    • Method Detail

      • calculateMaximumFlow

        public void calculateMaximumFlow​(V source,
                                         V sink)
        Sets current source to source, current sink to sink, then calculates maximum flow from source to sink. Note, that source and sink must be vertices of the network passed to the constructor, and they must be different.
        Parameters:
        source - source vertex
        sink - sink vertex
      • getMaximumFlowValue

        public java.lang.Double getMaximumFlowValue()
        Returns maximum flow value, that was calculated during last calculateMaximumFlow call, or null, if there was no calculateMaximumFlow calls.
        Returns:
        maximum flow value
      • getMaximumFlow

        public java.util.Map<E,​java.lang.Double> getMaximumFlow()
        Returns maximum flow, that was calculated during last calculateMaximumFlow call, or null, if there was no calculateMaximumFlow calls.
        Returns:
        read-only mapping from edges to doubles - flow values
      • getCurrentSource

        public V getCurrentSource()
        Returns current source vertex, or null if there was no calculateMaximumFlow calls.
        Returns:
        current source
      • getCurrentSink

        public V getCurrentSink()
        Returns current sink vertex, or null if there was no calculateMaximumFlow calls.
        Returns:
        current sink