Class StronglyConnectedComponents
public class StronglyConnectedComponents extends Object
The compute(ImmutableGraph, boolean, ProgressLogger)
method of this class will return
an instance that contains the data computed by running a variant of Tarjan's algorithm on an immutable graph.
The implementation is iterative, rather than recursive, to work around known limitations on the size of
the stack in current JVMs.
Besides the usually strongly connected components, it is possible to compute the buckets of the
graph, that is, nodes belonging to components that are terminal, but not dangling, in the component DAG.
After getting an instance, it is possible to run the computeSizes()
and sortBySize(int[])
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.

Field Summary
Fields Modifier and Type Field Description LongArrayBitVector
buckets
The bit vector for buckets, ornull
, in which case buckets have not been computed.int[]
component
The component of each node.int
numberOfComponents
The number of strongly connected components. 
Constructor Summary
Constructors Modifier Constructor Description protected
StronglyConnectedComponents(int numberOfComponents, int[] status, LongArrayBitVector buckets)

Method Summary
Modifier and Type Method Description static StronglyConnectedComponents
compute(ImmutableGraph graph, boolean computeBuckets, ProgressLogger pl)
Computes the strongly connected components of a given graph.static StronglyConnectedComponents
compute(ArcLabelledImmutableGraph graph, Transform.LabelledArcFilter filter, boolean computeBuckets, ProgressLogger pl)
Computes the strongly connected components of a given arclabelled graph, filtering its arcs.int[]
computeSizes()
Returns the size array for this set of strongly connected components.static void
main(String[] arg)
void
sortBySize(int[] size)
Renumbers by decreasing size the components of this set.

Field Details

numberOfComponents
public final int numberOfComponentsThe number of strongly connected components. 
component
public final int[] componentThe component of each node. 
buckets
The bit vector for buckets, ornull
, in which case buckets have not been computed.


Constructor Details

StronglyConnectedComponents
protected StronglyConnectedComponents(int numberOfComponents, int[] status, LongArrayBitVector buckets)


Method Details

compute
public static StronglyConnectedComponents compute(ImmutableGraph graph, boolean computeBuckets, ProgressLogger pl)Computes the strongly connected components of a given graph. Parameters:
graph
 the graph whose strongly connected components are to be computed.computeBuckets
 if true, buckets will be computed.pl
 a progress logger, ornull
. Returns:
 an instance of this class containing the computed components.

compute
public static StronglyConnectedComponents compute(ArcLabelledImmutableGraph graph, Transform.LabelledArcFilter filter, boolean computeBuckets, ProgressLogger pl)Computes the strongly connected components of a given arclabelled graph, filtering its arcs. Parameters:
graph
 the arclabelled graph whose strongly connected components are to be computed.filter
 a filter selecting the arcs that must be taken into consideration.computeBuckets
 if true, buckets will be computed.pl
 a progress logger, ornull
. Returns:
 an instance of this class containing the computed components.

computeSizes
public int[] computeSizes()Returns the size array for this set of strongly connected components. Returns:
 the size array for this set of strongly connected components.

sortBySize
public void sortBySize(int[] 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 array are permuted so that the sizes of strongly connected components are decreasing in the component index.
 Parameters:
size
 the components sizes, as returned bycomputeSizes()
.

main
 Throws:
IOException
JSAPException
