Class ConnectedComponents

java.lang.Object
it.unimi.dsi.big.webgraph.algo.ConnectedComponents

public class ConnectedComponents
extends Object
Computes the connected components of a symmetric (a.k.a. undirected) graph using a parallel breadth-first visit.

The compute(ImmutableGraph, int, ProgressLogger) method of this class will return an instance that contains the data computed by visiting the graph (using an instance of ParallelBreadthFirstVisit). Note that it is your responsibility to pass a symmetric graph to compute(ImmutableGraph, int, ProgressLogger). Otherwise, results will be unpredictable.

After getting an instance, it is possible to run the computeSizes() and sortBySize(long[][]) methods to obtain further information. This scheme has been devised to exploit the available memory as much as possible—after the components have been computed, the returned instance keeps no track of the graph, and the related memory can be freed by the garbage collector.

Performance issues

This class uses an instance of ParallelBreadthFirstVisit to ensure a high degree of parallelism (see its documentation for memory requirements).

  • Field Details

    • numberOfComponents

      public final long numberOfComponents
      The number of connected components.
    • component

      public final long[][] component
      The component of each node.
  • Constructor Details

    • ConnectedComponents

      protected ConnectedComponents​(long numberOfComponents, long[][] component)
  • Method Details

    • compute

      public static ConnectedComponents compute​(ImmutableGraph symGraph, int threads, ProgressLogger pl)
      Computes the connected components of a symmetric graph.
      Parameters:
      symGraph - a symmetric graph.
      threads - the requested number of threads (0 for Runtime.availableProcessors()).
      pl - a progress logger, or null.
      Returns:
      an instance of this class containing the computed components.
    • computeSizes

      public long[][] computeSizes()
      Returns the size big array for this set of strongly connected components.
      Returns:
      the size big array for this set of strongly connected components.
    • sortBySize

      public void sortBySize​(long[][] size)
      Renumbers by decreasing size the components of this set.

      After a call to this method, both the internal status of this class and the argument big array are permuted so that the sizes of strongly connected components are decreasing in the component index.

      Parameters:
      size - the components sizes, as returned by computeSizes().
    • main

      public static void main​(String[] arg) throws IOException, JSAPException
      Throws:
      IOException
      JSAPException