
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=string output=name cut=name [afcolumn=name] [abcolumn=name] source_layer=string [source_cats=range] [source_where=sql_query] sink_layer=string [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
- Data source for direct OGR access
- layer=string
- Layer number or name
- A single vector map can be connected to multiple database tables. This number determines which table to use. Layer name for direct OGR access.
- 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=string
- Source layer number or name
- A single vector map can be connected to multiple database tables. This number determines which table to use. Layer name for direct OGR access.
- 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=string
- Sink layer number or name
- A single vector map can be connected to multiple database tables. This number determines which table to use. Layer name for direct OGR access.
- 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 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: 2010-04-10 10:01:48 -0700 (Sat, 10 Apr 2010) $
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