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 ANYINTEGER and ANYNUMERICAL
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 

SQL query as described above. 
root vertex 

Identifier of the starting vertex. 
Inner query¶
Column 
Type 
Default 
Description 

id 

Identifier of the edge. 

source 

Identifier of the first end point vertex of the edge. 

target 

Identifier of the second end point vertex of the edge. 

cost 

Weight of the edge (source, target)


reverse_cost 

1 
Weight of the edge (target, source),

Where:
 ANYINTEGER
SMALLINT, INTEGER, BIGINT
 ANYNUMERICAL
SMALLINT, INTEGER, BIGINT, REAL, FLOAT
Result Columns¶
Returns set of (seq, vertex_id,idom)
Column 
Type 
Description 

seq 

Sequential value starting from 1. 
vertex_id 

Identifier of vertex . 
idom 

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¶
Sample Data network.
Indices and tables