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v.net.flow - Computes the maximum flow between two sets of nodes in the network.
vector, network, flow
v.net.flow v.net.flow --help v.net.flow input=name [arc_layer=string] [node_layer=string] output=name cut=name [arc_column=name] [arc_backward_column=name] [node_column=name] [source_cats=range] [source_where=sql_query] [sink_cats=range] [sink_where=sql_query] [--overwrite] [--help] [--verbose] [--quiet] [--ui] Flags: --overwrite Allow output files to overwrite existing files --help Print usage summary --verbose Verbose module output --quiet Quiet module output --ui Force launching GUI dialog Parameters: input=name [required] Name of input vector map Or data source for direct OGR access arc_layer=string Arc layer Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name. Default: 1 node_layer=string Node layer Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name. Default: 2 output=name [required] Name for output vector map cut=name [required] Name for output vector map containing a minimum cut arc_column=name Arc forward/both direction(s) cost column (number) arc_backward_column=name Arc backward direction cost column (number) node_column=name Node cost column (number) 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 population >= 10000 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 population >= 10000
v.net.flow computes the maximum flow and minimum cut between two sets of nodes.
The two sets of nodes are called sources and sink and v.net.flow finds the maximum flow from the former to the latter ones. Edge capacities can be specified by arc_column for forward direction and arc_backward_column for backward direction. If the latter parameter is omitted 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.
Find maximum flow from factories to stores using SPEED for the capacities. v.net.flow input=roads output=roads_flow cut=roads_cut arc_column=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 arc_column=ones \ source_cats=1-10 sink_cats=100-100
Daniel Bundala, Google Summer of Code 2009, Student Wolf Bergenheim, Mentor Last changed: $Date: 2016-08-30 15:28:34 +0200 (Tue, 30 Aug 2016) $
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