pgr_lengauerTarjanDominatorTree -Experimental

pgr_lengauerTarjanDominatorTree - Returns the immediate dominator of all vertices.

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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

  • Version 3.2.0

    • New experimental function

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 dominator tree with root vertex \(5\) 

SELECT * FROM pgr_lengauertarjandominatortree(
  $$SELECT id,source,target,cost,reverse_cost FROM edges$$,
  5) ORDER BY vertex_id;
 seq  vertex_id  idom
-----+-----------+------
   1          1     2
   9          2     0
   2          3     3
  10          4     0
  17          5     0
   4          6    17
   3          7     4
   7          8     3
  11          9     7
   5         10    16
   6         11     3
   8         12     3
  12         13     0
  13         14     0
  16         15    15
  15         16     3
  14         17     3
(17 rows)

Parameters

Column

Type

Description

Edges SQL

TEXT

SQL query as described above.

root vertex

BIGINT

Identifier of the starting vertex.

Inner Queries

Edges SQL

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 )

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

Example :

Dominator tree of another component. 

SELECT * FROM pgr_lengauertarjandominatortree(
  $$SELECT id,source,target,cost,reverse_cost FROM edges$$,
  13) ORDER BY vertex_id;
 seq  vertex_id  idom
-----+-----------+------
   1          1     0
   9          2     0
   2          3     0
  10          4     0
  17          5     0
   4          6     0
   3          7     0
   7          8     0
  11          9     0
   5         10     0
   6         11     0
   8         12     0
  12         13     0
  13         14    12
  16         15     0
  15         16     0
  14         17     0
(17 rows)

See Also

Indices and tables