build.paths: Functions for managing shortest paths
In travelr: Functions for Travel Demand Modeling

Description Usage Arguments Details Value Author(s) See Also

Build shortest paths from an assignment set and load demands on the paths

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build.paths(aset,costs)
build.and.load.paths(aset,costs)
load.paths(aset,paths)

`aset`	An `assignment.set`
`costs`	A vector or matrix of costs for the network. Unused links may be zero or NA.
`paths`	A `path.set` build by `build.paths`

These functions are used to support link-based highway assignment algorithms, as well as operations on path sets resulting from highway assignment. build.paths makes a path set given a set of costs. The first application of build.paths is usually performed using zero volumes, corresponding to a free-flow condition. See free.flow.

With the resulting paths, the load.paths function will place the demand matrix onto the network links according to the shortest paths. This corresponds to an all-or-nothing assignment. It differs from the “AON” highway assignment method in that it does not diagnostic checking and has a simpler set of parameters.

build.and.load.paths performs a build.paths operation followed directly by the equivalent of load.paths.

The result of both load.paths and build.and.load.paths is a data.frame with one numeric column of link volumes per assignment class. The names of the resulting data.frame of volumes correspond to the names of the assignment classes.

In general, particularly when testing new code, it is preferable to build all-or-nothing volumes by using highway.assign( aset, method="AON" ) rather than calling build.and.load.paths directly, since more error-checking will occur.

The costs for path building are a link vector or a list or data.frame with one column per assignment class, and one row for each link in the network. See assignment.set for details. Ordinarily the costs are constructed by passing the link volumes to the cost.function stored within the assignment set.

build.paths constructs a path set, using a vector of costs that should have been built by the cost.function associated with the assignment.set. load.paths constructs a data.frame with one numeric column of link volumes per assignment class build.and.load.paths returns a list consisting of the loaded volumes (the same as load.paths) and the corresponding path set as would have been returned from build.paths

Jeremy Raw

highway.assign for general equilibrium assignment methods for highway networks.

assignment.set for information about how to assemble assignment sets.

free.flow for free-flow volumes.

travelr documentation built on May 2, 2019, 5:17 p.m.