pgr_kruskalDFS - pgRouting Manual (3.4)

Description

Visits and extracts the nodes information in Depth First Search ordering of the Minimum Spanning Tree created using Kruskal’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.

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

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

• Returned tree nodes from a root vertex are on Depth First Search order

• Depth First Search Running time: \(O(E + V)\)

Signatures

SELECT * FROM pgr_kruskalDFS(
  'SELECT id, source, target, cost, reverse_cost FROM edges ORDER BY id',
  6);
 seq  depth  start_vid  node  edge  cost  agg_cost
-----+-------+-----------+------+------+------+----------
   1      0          6     6    -1     0         0
   2      1          6     5     1     1         1
   3      1          6    10     2     1         1
   4      2          6    15     3     1         2
   5      3          6    16    16     1         3
   6      4          6    17    15     1         4
   7      5          6    12    13     1         5
   8      6          6    11    11     1         6
   9      6          6     8    12     1         6
  10      7          6     7    10     1         7
  11      8          6     3     7     1         8
  12      9          6     1     6     1         9
  13      7          6     9    14     1         7
(13 rows)

SELECT * FROM pgr_kruskalDFS(
  'SELECT id, source, target, cost, reverse_cost FROM edges ORDER BY id',
  ARRAY[9, 6], max_depth => 3);
 seq  depth  start_vid  node  edge  cost  agg_cost
-----+-------+-----------+------+------+------+----------
   1      0          6     6    -1     0         0
   2      1          6     5     1     1         1
   3      1          6    10     2     1         1
   4      2          6    15     3     1         2
   5      3          6    16    16     1         3
   6      0          9     9    -1     0         0
   7      1          9     8    14     1         1
   8      2          9     7    10     1         2
   9      3          9     3     7     1         3
  10      2          9    12    12     1         2
  11      3          9    11    11     1         3
  12      3          9    17    13     1         3
(12 rows)

Parameters

Where:

ANY-INTEGER :

SMALLINT, INTEGER, BIGINT

ANY-NUMERIC :

SMALLINT, INTEGER, BIGINT, REAL, FLOAT, NUMERIC

Inner Queries

Result Columns

Returns SET OF (seq, depth, start_vid, node, edge, cost, agg_cost)

Where:

ANY-INTEGER :

SMALLINT, INTEGER, BIGINT

ANY-NUMERIC :

SMALLINT, INTEGER, BIGINT, REAL, FLOAT, NUMERIC

See Also

• Spanning Tree - Category

• Kruskal - Family of functions

• Sample Data

• Boost: Kruskal’s algorithm

• Wikipedia: Kruskal’s algorithm

Indices and tables

• Index

• Search Page