pgr_lineGraph - Experimental

pgr_lineGraph — Transforms the given graph into its corresponding edge-based graph.

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 2.5.0

  • New Experimental function

Description

Given a graph \(G\), its line graph \(L(G)\) is a graph such that:

• Each vertex of \(L(G)\) represents an edge of \(G\).

• Two vertices of \(L(G)\) are adjacent if and only if their corresponding edges share a common endpoint in \(G\)

The main characteristics are:

• Works for directed and undirected graphs.

• The cost and reverse_cost columns of the result represent existence of the edge.

• When the graph is directed the result is directed.

• When the graph is undirected the result is undirected.

  • The reverse_cost is always \(-1\).

Signatures

pgr_lineGraph(Edges SQL, [directed])

Returns set of (seq, source, target, cost, reverse_cost)

OR EMPTY SET

Example:

For an undirected graph with edges :math:’{2,4,5,8}’

SELECT * FROM pgr_lineGraph(
  'SELECT id, source, target, cost, reverse_cost FROM edges'
);
 seq | source | target | cost | reverse_cost
-----+--------+--------+------+--------------
   1 |    -18 |     18 |    1 |            1
   2 |    -17 |     17 |    1 |            1
   3 |    -16 |     -3 |    1 |           -1
   4 |    -14 |    -10 |    1 |            1
   5 |    -14 |     12 |    1 |           -1
   6 |    -14 |     14 |    1 |            1
   7 |    -10 |     -7 |    1 |            1
   8 |    -10 |     -4 |    1 |            1
   9 |    -10 |      8 |    1 |            1
  10 |    -10 |     10 |    1 |            1
  11 |     -9 |     -8 |    1 |            1
  12 |     -9 |      9 |    1 |            1
  13 |     -9 |     11 |    1 |           -1
  14 |     -8 |     -7 |    1 |            1
  15 |     -8 |     -4 |    1 |            1
  16 |     -8 |      8 |    1 |            1
  17 |     -7 |     -6 |    1 |            1
  18 |     -7 |      7 |    1 |            1
  19 |     -6 |      6 |    1 |            1
  20 |     -3 |     -2 |    1 |           -1
  21 |     -3 |      5 |    1 |           -1
  22 |     -2 |     -1 |    1 |           -1
  23 |     -2 |      4 |    1 |           -1
  24 |      1 |     -1 |    1 |            1
  25 |      1 |      4 |    1 |            1
  26 |      4 |     -7 |    1 |            1
  27 |      4 |     -4 |    1 |            1
  28 |      5 |     -8 |    1 |           -1
  29 |      5 |      9 |    1 |           -1
  30 |      5 |     11 |    1 |           -1
  31 |      8 |     11 |    1 |           -1
  32 |      9 |    -16 |    1 |            1
  33 |      9 |     15 |    1 |            1
  34 |     10 |     12 |    1 |           -1
  35 |     11 |     13 |    1 |           -1
  36 |     12 |     13 |    1 |           -1
  37 |     13 |    -15 |    1 |           -1
  38 |     15 |    -15 |    1 |            1
  39 |     16 |    -16 |    1 |            1
  40 |     16 |     15 |    1 |            1
(40 rows)

Parameters

Parameter	Type	Description
Edges SQL	TEXT	Edges SQL as described below.

Optional parameters

Column	Type	Default	Description
directed	BOOLEAN	true	When true the graph is considered Directed When false the graph is considered as Undirected.

Inner Queries

Edges SQL

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)
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, source, target, cost, reverse_cost)

Column	Type	Description
seq	INTEGER	Sequential value starting from 1. Gives a local identifier for the edge
source	BIGINT	Identifier of the source vertex of the current edge. When negative: the source is the reverse edge in the original graph.
target	BIGINT	Identifier of the target vertex of the current edge. When negative: the target is the reverse edge in the original graph.
cost	FLOAT	Weight of the edge (source, target). When negative: edge (source, target) does not exist, therefore it’s not part of the graph.
reverse_cost	FLOAT	Weight of the edge (target, source). When negative: edge (target, source) does not exist, therefore it’s not part of the graph.

See Also

• wikipedia: Line Graph

• mathworld: Line Graph

• Sample Data

Indices and tables

• Index

• Search Page