pgr_lengauerTarjanDominatorTree -Experimental¶

pgr_lengauerTarjanDominatorTree — Returns the immediate dominator of all vertices.

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) -- Experimental on v3.2
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.

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)