pgr_maxFlow

pgr_maxFlow — Calculates the maximum flow in a directed graph from the source(s) to the targets(s) using the Push Relabel algorithm.

_images/boost-inside.jpeg

Boost Graph Inside

Availability

  • Version 3.0.0
    • Official function
  • Version 2.4.0
    • New Proposed function

Support

Description

The main characteristics are:

  • The graph is directed.
  • Calculates the maximum flow from the source(s) to the target(s).
    • When the maximum flow is 0 then there is no flow and 0 is returned.
    • There is no flow when a source is the same as a target.
  • Any duplicated value in the source(s) or target(s) are ignored.
  • Uses the pgr_pushRelabel algorithm.
  • Running time: \(O( V ^ 3)\)

Signatures

Summary

pgr_maxFlow(Edges SQL, source,  target)
pgr_maxFlow(Edges SQL, sources,  target)
pgr_maxFlow(Edges SQL, source,  targets)
pgr_maxFlow(Edges SQL, sources,  targets)
RETURNS BIGINT

One to One

pgr_maxFlow(Edges SQL, source,  target)
RETURNS BIGINT
Example:From vertex \(6\) to vertex \(11\)
SELECT * FROM pgr_maxFlow(
    'SELECT id,
            source,
            target,
            capacity,
            reverse_capacity
    FROM edge_table'
    , 6, 11
);
 pgr_maxflow
-------------
         230
(1 row)

One to Many

pgr_maxFlow(Edges SQL, source,  targets)
RETURNS BIGINT
Example:From vertex \(6\) to vertices \(\{11, 1, 13\}\)
SELECT * FROM pgr_maxFlow(
    'SELECT id,
            source,
            target,
            capacity,
            reverse_capacity
    FROM edge_table'
    , 6, ARRAY[11, 1, 13]
);
 pgr_maxflow
-------------
         340
(1 row)

Many to One

pgr_maxFlow(Edges SQL, sources,  target)
RETURNS BIGINT
Example:From vertices \(\{6, 8, 12\}\) to vertex \(11\)
SELECT * FROM pgr_maxFlow(
    'SELECT id,
            source,
            target,
            capacity,
            reverse_capacity
    FROM edge_table'
    , ARRAY[6, 8, 12], 11
);
 pgr_maxflow
-------------
         230
(1 row)

Many to Many

pgr_maxFlow(Edges SQL, sources,  targets)
RETURNS BIGINT
Example:From vertices \(\{6, 8, 12\}\) to vertices \(\{1, 3, 11\}\)
SELECT * FROM pgr_maxFlow(
    'SELECT id,
            source,
            target,
            capacity,
            reverse_capacity
    FROM edge_table'
    , ARRAY[6, 8, 12], ARRAY[1, 3, 11]
);
 pgr_maxflow
-------------
         360
(1 row)

Parameters

Column Type Default Description
Edges SQL TEXT   The edges SQL query as described in Inner Query.
source BIGINT   Identifier of the starting vertex of the flow.
sources ARRAY[BIGINT]   Array of identifiers of the starting vertices of the flow.
target BIGINT   Identifier of the ending vertex of the flow.
targets ARRAY[BIGINT]   Array of identifiers of the ending vertices of the flow.

Inner query

Edges SQL:an SQL query of a directed graph of capacities, which should return a set of rows with the following columns:
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.
capacity ANY-INTEGER  

Weight of the edge (source, target)

  • When negative: edge (source, target) does not exist, therefore it’s not part of the graph.
reverse_capacity ANY-INTEGER -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

Return Columns

Type Description
BIGINT Maximum flow possible from the source(s) to the target(s)