pgr_prim

pgr_prim — Minimum spanning forest of graph using Prim algorithm.

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Boost Graph Inside

Availability

  • Version 3.0.0

    • New Official function

Support

  • Supported versions: current(3.0)

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.