pgr_lengauerTarjanDominatorTree -Experimental

pgr_lengauerTarjanDominatorTree — Returns the immediate dominator of all vertices.

_images/boost-inside.jpeg

Boost Graph Inside

Warning

Possible server crash

  • These functions might create a server crash

Warning

Experimental functions

  • They are not officially of the current release.
  • They likely will not be officially be part of the next release:
    • The functions might not make use of ANY-INTEGER and ANY-NUMERICAL
    • Name might change.
    • Signature might change.
    • Functionality might change.
    • pgTap tests might be missing.
    • Might need c/c++ coding.
    • May lack documentation.
    • Documentation if any might need to be rewritten.
    • Documentation examples might need to be automatically generated.
    • Might need a lot of feedback from the comunity.
    • Might depend on a proposed function of pgRouting
    • Might depend on a deprecated function of pgRouting

Availability

Description

The algorithm calculates the immidiate dominator of each vertex called idom, once idom of each vertex is calculated then by making every idom of each vertex as its parent, the dominator tree can be built.

The main Characteristics are:

  • The algorithm works in directed graph only.
  • The returned values are not ordered.
  • The algorithm returns idom of each vertex.
  • If the root vertex not present in the graph then it returns empty set.
  • Running time: \(O((V+E)log(V+E))\)

Signatures

Summary

pgr_lengauerTarjanDominatorTree(Edges SQL, root vertex)
RETURNS SET OF (seq, vertex_id, idom)
OR EMPTY SET
Example:The lengauerTarjanDominatorTree with root vertex \(1\)
   SELECT * FROM pgr_lengauertarjandominatortree(
    $$SELECT id,source,target,cost,reverse_cost FROM edge_table$$,
    1
);
 seq | vertex_id | idom
-----+-----------+------
   1 |         1 |    0
   2 |         2 |    1
   3 |         3 |    4
   4 |         4 |    9
   5 |         5 |    2
   6 |         6 |    5
   7 |         7 |    8
   8 |         8 |    5
   9 |         9 |    5
  10 |        10 |    5
  11 |        11 |    5
  12 |        12 |    5
  13 |        13 |   10
  14 |        14 |    0
  15 |        15 |    0
  16 |        16 |    0
  17 |        17 |    0
(17 rows)

Parameters

Column Type Description
Edges SQL TEXT SQL query as described above.
root vertex BIGINT Identifier of the starting vertex.

Inner query

Column Type Default Description
id ANY-INTEGER   Identifier of the edge.
source ANY-INTEGER   Identifier of the first end point vertex of the edge.
target ANY-INTEGER   Identifier of the second end point vertex of the edge.
cost ANY-NUMERICAL  

Weight of the edge (source, target)

  • When negative: edge (source, target) does not exist, therefore it’s not part of the graph.
reverse_cost ANY-NUMERICAL -1

Weight of the edge (target, source),

  • When negative: edge (target, source) does not exist, therefore it’s not part of the graph.

Where:

ANY-INTEGER:SMALLINT, INTEGER, BIGINT
ANY-NUMERICAL:SMALLINT, INTEGER, BIGINT, REAL, FLOAT

Result Columns

Returns set of (seq, vertex_id,idom)

Column Type Description
seq INTEGER Sequential value starting from 1.
vertex_id BIGINT Identifier of vertex .
idom BIGINT Immediate dominator of vertex.

Additional Examples

The examples in this section use the following Network for queries marked as directed and cost and reverse_cost columns are used

Example:When the edge is disonnectd from graph then it will returns immidiate dominator of all other vertex as zero.
   SELECT * FROM pgr_lengauertarjandominatortree(
    $$SELECT id,source,target,cost,reverse_cost FROM edge_table$$,
    16
);
 seq | vertex_id | idom
-----+-----------+------
   1 |         1 |    0
   2 |         2 |    0
   3 |         3 |    0
   4 |         4 |    0
   5 |         5 |    0
   6 |         6 |    0
   7 |         7 |    0
   8 |         8 |    0
   9 |         9 |    0
  10 |        10 |    0
  11 |        11 |    0
  12 |        12 |    0
  13 |        13 |    0
  14 |        14 |    0
  15 |        15 |    0
  16 |        16 |    0
  17 |        17 |   16
(17 rows)