# pgRouting Manual (3.1)

## Kruskal - Family of functions

- pgr_kruskal

- pgr_kruskalBFS

- pgr_kruskalDD

- pgr_kruskalDFS

Boost Graph Inside

Previous versions of this page

- Supported versions: current(3.1) 3.0

## Description

Kruskal’s algorithm is a greedy minimum spanning tree algorithm that in each cycle finds and adds the edge of the least possible weight that connects any two trees in the forest.

The main Characteristics are:

- It’s implementation is only on undirected graph.

- Process is done only on edges with positive costs.

- The total weight of all the edges in the tree or forest is minimized.

- 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.

- Kruskal’s running time: \(O(E * log E)\)

## 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

## See Also

- Spanning Tree - Category

- Boost: Kruskal’s algorithm documentation

- Wikipedia: Kruskal’s algorithm

Indices and tables

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