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

  • 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 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)

See Also

Indices and tables