pgr_prim

pgr_prim - Minimum spanning forest of graph using Prim algorithm.

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Availability

  • Version 3.0.0

    • New Official function

Support

Description

This algorithm finds the minimum spanning forest in a possibly disconnected graph using Prim’s algorithm.

The main characteristics are:

  • It’s implementation is only on undirected graph .

  • Process is done only on edges with positive costs.

  • When the graph is connected

    • The resulting edges make up a tree

  • When the graph is not connected,

    • Finds a minimum spanning tree for each connected component.

    • The resulting edges make up a forest.

  • Prim’s running time: \(O(E*log V)\)

  • EMPTY SET is returned when there are no edges in the graph.

Signatures

Summary

pgr_prim(edges_sql)

RETURNS SET OF (edge, cost)
OR EMPTY SET
Example :

Minimum Spanning Forest of a subgraph

SELECT edge, cost FROM pgr_prim(
    'SELECT id, source, target, cost, reverse_cost FROM edge_table WHERE id < 14'
) ORDER BY edge;
 edge  cost
------+------
    1     1
    2     1
    3     1
    4     1
    5     1
    6     1
    7     1
    9     1
   10     1
   11     1
   13     1
(11 rows)

Parameters

Parameter

Type

Description

Edges SQL

TEXT

SQL query described in Inner query .

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 (edge, cost)

Column

Type

Description

edge

BIGINT

Identifier of the edge.

cost

FLOAT

Cost to traverse the edge.

See Also

Indices and tables