# pgr_articulationPoints - Experimental¶

pgr_articulationPoints - Return the articulation points of an undirected graph. In particular, the algorithm implemented by Boost.Graph.

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

## Synopsis¶

Those vertices that belong to more than one biconnected component are called articulation points or, equivalently, cut vertices. Articulation points are vertices whose removal would increase the number of connected components in the graph. This implementation can only be used with an undirected graph.

## Characteristics¶

The main Characteristics are:

• The returned values are ordered:
• node ascending
• Running time: $$O(V + E)$$

## Signatures¶

pgr_articulationPoints(edges_sql)

RETURNS SET OF (seq, node)
OR EMPTY SET


The signature is for a undirected graph.

SELECT * FROM pgr_articulationPoints(
'SELECT id, source, target, cost, reverse_cost FROM edge_table'
);
seq | node
-----+------
1 |    2
2 |    5
3 |    8
4 |   10
(4 rows)



## Description of the Signatures¶

### Description of the edges_sql query for components functions¶

edges_sql: an SQL query, which should return a set of rows with the following columns:
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 SMALLINT, INTEGER, BIGINT, REAL, FLOAT

### Description of the parameters of the signatures¶

Parameter Type Default Description
edges_sql TEXT   SQL query as described above.

### Description of the return values for articulation points¶

Returns set of (seq, node)

Column Type Description
seq INT Sequential value starting from 1.
node BIGINT Identifier of the vertex.