pgr_maxFlowMinCost - Experimental

pgr_maxFlowMinCost - Calculates the flow on the graph edges that maximizes the flow and minimizes the cost from the sources to the targets.

images/boost-inside.jpeg

Boost Graph Inside

Warning

Possible server crash

  • These functions might create a server crash

Warning

Experimental functions

  • They are not officially of the current release.

  • They likely will not be officially be part of the next release:

    • The functions might not make use of ANY-INTEGER and ANY-NUMERICAL

    • Name might change.

    • Signature might change.

    • Functionality might change.

    • pgTap tests might be missing.

    • Might need c/c++ coding.

    • May lack documentation.

    • Documentation if any might need to be rewritten.

    • Documentation examples might need to be automatically generated.

    • Might need a lot of feedback from the comunity.

    • Might depend on a proposed function of pgRouting

    • Might depend on a deprecated function of pgRouting

Availability

  • Version 3.2.0

    • New experimental function:

      • pgr_maxFlowMinCost(Combinations)

  • Version 3.0.0

  • New experimental function

Description

The main characteristics are:

  • The graph is directed .

  • Process is done only on edges with positive capacities.

  • When the maximum flow is 0 then there is no flow and EMPTY SET 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.

  • Calculates the flow/residual capacity for each edge. In the output

    • Edges with zero flow are omitted.

  • Creates a super source and edges to all the source(s), and a super target and the edges from all the targets(s).

  • The maximum flow through the graph is guaranteed to be the value returned by pgr_maxFlow when executed with the same parameters and can be calculated:

    • By aggregation of the outgoing flow from the sources

    • By aggregation of the incoming flow to the targets

  • TODO check which statement is true:

    • The cost value of all input edges must be nonnegative.

    • Process is done when the cost value of all input edges is nonnegative.

    • Process is done on edges with nonnegative cost.

  • Running time: \(O(U * (E + V * logV))\)

    • where \(U\) is the value of the max flow.

    • \(U\) is upper bound on number of iterations. In many real world cases number of iterations is much smaller than \(U\) .

Signatures

Summary 

pgr_maxFlowMinCost(Edges SQL, source,  target)
pgr_maxFlowMinCost(Edges SQL, sources, target)
pgr_maxFlowMinCost(Edges SQL, source,  targets)
pgr_maxFlowMinCost(Edges SQL, sources, targets)
pgr_maxFlowMinCost(Edges SQL, Combinations SQL) -- Experimental on v3.2
RETURNS SET OF (seq, edge, source, target, flow, residual_capacity, cost, agg_cost)
OR EMPTY SET

One to One 

pgr_maxFlowMinCost(Edges SQL, source, target)
RETURNS SET OF (seq, edge, source, target, flow, residual_capacity, cost, agg_cost)
OR EMPTY SET
Example :

From vertex \(2\) to vertex \(3\) 

SELECT * FROM pgr_MaxFlowMinCost(
    'SELECT id,
     source, target,
     capacity, reverse_capacity,
     cost, reverse_cost FROM edge_table',
    2, 3
);
 seq  edge  source  target  flow  residual_capacity  cost  agg_cost
-----+------+--------+--------+------+-------------------+------+----------
   1     4       2       5    80                 20    80        80
   2     3       4       3    80                 50    80       160
   3     8       5       6    80                 20    80       240
   4     9       6       9    80                 50    80       320
   5    16       9       4    80                  0    80       400
(5 rows)

One to Many 

pgr_maxFlowMinCost(Edges SQL, source, targets)
RETURNS SET OF (seq, edge, source, target, flow, residual_capacity, cost, agg_cost)
OR EMPTY SET
Example :

From vertex \(13\) to vertices \(\{7, 1, 4\}\) 

SELECT * FROM pgr_MaxFlowMinCost(
    'SELECT id,
     source, target,
     capacity, reverse_capacity,
     cost, reverse_cost FROM edge_table',
    13, ARRAY[7, 1, 4]
);
 seq  edge  source  target  flow  residual_capacity  cost  agg_cost
-----+------+--------+--------+------+-------------------+------+----------
   1     1       2       1    50                 80    50        50
   2     4       5       2    50                  0    50       100
   3    16       9       4    50                 30    50       150
   4    10      10       5    50                  0    50       200
   5    12      10      11    50                 50    50       250
   6    13      11      12    50                 50    50       300
   7    15      12       9    50                  0    50       350
   8    14      13      10   100                 30   100       450
(8 rows)

Many to One 

pgr_maxFlowMinCost(Edges SQL, sources, target)
RETURNS SET OF (seq, edge, source, target, flow, residual_capacity, cost, agg_cost)
OR EMPTY SET
Example :

From vertices \(\{1, 7, 14\}\) to vertex \(12\) 

SELECT * FROM pgr_MaxFlowMinCost(
    'SELECT id,
     source, target,
     capacity, reverse_capacity,
     cost, reverse_cost FROM edge_table',
    ARRAY[1, 7, 14], 12
);
 seq  edge  source  target  flow  residual_capacity  cost  agg_cost
-----+------+--------+--------+------+-------------------+------+----------
   1     1       1       2    80                  0    80        80
   2     4       2       5    80                 20    80       160
   3     8       5       6   100                  0   100       260
   4    10       5      10    30                100    30       290
   5     9       6       9    50                 80    50       340
   6    11       6      11    50                 80    50       390
   7     6       7       8    50                  0    50       440
   8     7       8       5    50                  0    50       490
   9    15       9      12    50                 30    50       540
  10    12      10      11    30                 70    30       570
  11    13      11      12    80                 20    80       650
(11 rows)

Many to Many 

pgr_maxFlowMinCost(Edges SQL, sources, targets)
RETURNS SET OF (seq, edge, source, target, flow, residual_capacity, cost, agg_cost)
OR EMPTY SET
Example :

From vertices \(\{7, 13\}\) to vertices \(\{3, 9\}\) 

SELECT * FROM pgr_MaxFlowMinCost(
    'SELECT id,
     source, target,
     capacity, reverse_capacity,
     cost, reverse_cost FROM edge_table',
    ARRAY[7, 13], ARRAY[3, 9]
);
 seq  edge  source  target  flow  residual_capacity  cost  agg_cost
-----+------+--------+--------+------+-------------------+------+----------
   1     8       5       6   100                  0   100       100
   2     9       6       9   100                 30   100       200
   3     6       7       8    50                  0    50       250
   4     7       8       5    50                  0    50       300
   5    10      10       5    50                  0    50       350
   6    12      10      11    50                 50    50       400
   7    13      11      12    50                 50    50       450
   8    15      12       9    50                  0    50       500
   9    14      13      10   100                 30   100       600
(9 rows)

Combinations 

pgr_maxFlowMinCost(Edges SQL, Combinations SQL)
RETURNS SET OF (seq, edge, source, target, flow, residual_capacity, cost, agg_cost)
OR EMPTY SET
Example :

Using a combinations table, equivalent to calculating result from vertices \(\{7, 13\}\) to vertices \(\{3, 9\}\) . 

SELECT * FROM pgr_MaxFlowMinCost(
    'SELECT id,
     source, target,
     capacity, reverse_capacity,
     cost, reverse_cost FROM edge_table',
    'SELECT * FROM ( VALUES (7, 3), (13, 9) ) AS t(source, target)'
);
 seq  edge  source  target  flow  residual_capacity  cost  agg_cost
-----+------+--------+--------+------+-------------------+------+----------
   1     8       5       6   100                  0   100       100
   2     9       6       9   100                 30   100       200
   3     6       7       8    50                  0    50       250
   4     7       8       5    50                  0    50       300
   5    10      10       5    50                  0    50       350
   6    12      10      11    50                 50    50       400
   7    13      11      12    50                 50    50       450
   8    15      12       9    50                  0    50       500
   9    14      13      10   100                 30   100       600
(9 rows)

Parameters

Column

Type

Default

Description

Edges SQL

TEXT

Edges query as described in Inner Queries .

Combinations SQL

TEXT

Combinations query as described in Inner Queries .

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 queries

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

Capacity 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

Capacity of the edge (target, source) ,

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

cost

ANY-NUMERICAL

Weight of the edge (source, target) if it exists.

reverse_cost

ANY-NUMERICAL

0

Weight of the edge (target, source) if it exists.

Where:

ANY-INTEGER :

SMALLINT, INTEGER, BIGINT

ANY-NUMERICAL :

smallint, int, bigint, real, float

Combinations SQL :

an SQL query which should return a set of rows with the following columns:

Column

Type

Default

Description

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.

Where:

ANY-INTEGER :

SMALLINT, INTEGER, BIGINT

The function aggregates the sources and the targets, removes the duplicates, and then it calculates the result from the resultant source vertices to the target vertices.

Result Columns

Column

Type

Description

seq

INT

Sequential value starting from 1 .

edge

BIGINT

Identifier of the edge in the original query(edges_sql).

source

BIGINT

Identifier of the first end point vertex of the edge.

target

BIGINT

Identifier of the second end point vertex of the edge.

flow

BIGINT

Flow through the edge in the direction (source, target).

residual_capacity

BIGINT

Residual capacity of the edge in the direction (source, target).

cost

FLOAT

The cost of sending this flow through the edge in the direction (source, target).

agg_cost

FLOAT

The aggregate cost.

See Also

Indices and tables