NAME
v.net.flow - Computes the maximum flow between two sets of nodes in the network.
KEYWORDS
vector, network, flow
SYNOPSIS
v.net.flow
v.net.flow help
v.net.flow input=name [layer=integer] output=name cut=name [afcolumn=name] [abcolumn=name] [source_layer=integer] [source_cats=range] [source_where=sql_query] [sink_layer=integer] [sink_cats=range] [sink_where=sql_query] [--overwrite] [--verbose] [--quiet]
Flags:
- --overwrite
- Allow output files to overwrite existing files
- --verbose
- Verbose module output
- --quiet
- Quiet module output
Parameters:
- input=name
- Name of input vector map
- layer=integer
- Layer number
- A single vector map can be connected to multiple database tables. This number determines which table to use.
- Default: 1
- output=name
- Name for output vector map
- cut=name
- Name for output vector map containing a minimum cut
- afcolumn=name
- Name of arc forward/both direction(s) capacity column
- abcolumn=name
- Name of arc backward direction capacity column
- source_layer=integer
- Source layer number or name
- A single vector map can be connected to multiple database tables. This number determines which table to use.
- Default: 1
- source_cats=range
- Source category values
- Example: 1,3,7-9,13
- source_where=sql_query
- Source WHERE conditions of SQL statement without 'where' keyword
- Example: income < 1000 and inhab >= 10000
- sink_layer=integer
- Sink layer number or name
- A single vector map can be connected to multiple database tables. This number determines which table to use.
- Default: 1
- sink_cats=range
- Sink category values
- Example: 1,3,7-9,13
- sink_where=sql_query
- Sink WHERE conditions of SQL statement without 'where' keyword
- Example: income < 1000 and inhab >= 10000
DESCRIPTION
v.net.flow computes the maximum flow and minimum cut between
two sets of nodes.
NOTES
The two sets of nodes are called sources and sink and
v.net.flow finds the maximimum flow from the former to the
latter ones. Edge capacities can be specified by afcolumn for
forward direction and abcolumn for backward direction. If the
latter parameter is ommited then the same capacity is used in either
direction. The sets are given by the respective cats, layer
and where parameters. Maximum flow corresponds to the maximum
amount of water possibly flowing through the network preserving the
capacity constraints and minimum cut to the set of edges of minimum total
capacity completely separating sources from sinks. The cut produced by
this module corresponds to the first fully saturated edges from sources
to sinks. An attribute table containing the flow information is linked
to the output map. The table consists of two columns: cat
and flow and stores the flow along each line. Negative flow
means that "water" is flowing in the backward direction. Cut map
contains the edges in the minimum cut.
A famous result
says that the total amount of water flowing is equal to the minimum cut.
EXAMPLES
Find maximum flow from factories to stores using SPEED for the capacities.
v.net.flow input=roads output=roads_flow cut=roads_cut afcolumn=SPEED source_where="type=factory" sink_where="type=store"
If all the capacties are one then the minimum cut corresponds to the
minimum number of edges separating sources from sinks.
v.net.flow input=network output=flow cut=cut afcolumn=ones source_cats=1-10 sink_cats=100-100
SEE ALSO
v.net.connectivity
AUTHORS
Daniel Bundala, Google Summer of Code 2009, Student
Wolf Bergenheim, Mentor
Last changed: $Date: 2011-11-08 02:23:26 -0800 (Tue, 08 Nov 2011) $
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