# pgRouting Manual (2.5)

## pgr_articulationPoints - Experimental

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

Boost Graph Inside

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.

Example: |

    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
ANY-NUMERICAL: | 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.

## See Also

- http://en.wikipedia.org/wiki/Biconnected_component
- The queries use the Sample Data network.

Indices and tables

- Index
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