assignment.class: Building highway assignment classes
In travelr: Functions for Travel Demand Modeling

Description Usage Arguments Details Value Author(s) See Also

These functions facilitate constructing network variants and demand sets for use in multi-class highway assignment.

make.assignment.class(network, name, demand, link.subset=TRUE, penalty.subset=NULL, cost.function=NULL)
add.assignment.class(classes,aclass)
## S3 method for class 'list'
add.assignment.class(classes,aclass)

`network`	The base highway network on which this assignment set will be loaded
`name`	A name (character string) for the assignment class
`demand`	A demand matrix for the named assignment class
`link.subset`	An index vector that can be used to select links in the base network that will be available for this assignment class
`penalty.subset`	An index vector that selects which penalties (from the network's turn penalty table) will be applied to this assignment set
`cost.function`	A `cost.function` for the class. Not required or recommend; see details
`classes`	A list, either empty or containing previously added assignment classes
`aclass`	A highway.assignment.class constructed by `make.assignment.class`

These functions support multi-class highway assignment.

Use make.assignment.class to construct a new assignment class. Use add.assignment.class to add another assignment class to a list of assignment classes. A list of assignment classes is required for the classes parameter in new.assignment.set.

It is common to have a non-null link.subset, with the most common situation being to distinguish networks in which all links are available from one that only contains links available to a certain vehicle class (e.g. trucks or high-occupancy vehicles). It is similarly useful to have a non-null penalty.subset, either for penalties that are only applicable during certain periods of the day, or that are only applicable to certain vehicle classes. Only the links and penalties in the indicated subset will be examined when building paths. Care should be taken that the terminal nodes (zones) all remain connnected when the particular subset is selected. The igraph package can be useful for rapidly testing connectivity. The shortest path functions will warn if the resulting network subset is not connected.

The cost.function parameter is not used directly, but is provided as a convenience since it is sometimes desirable to decompose the cost.function for the assignment.set into smaller functions specifically for the individual classes. These can be called by the user's assignment set cost function. Getting fancy with cost functions is not advised since it can wreak havoc with the convergence of equilibrium assignment algorithms, and the simplest possible cost function model should be sought (which usually means providing a single function through new.assignment.set).

add.assignment.class is generic, and can add an assignment class to an assignment.set or to an existing list of assignment classes previously created with add.assignment.class. It performs a variety of tests to ensure that the proposed assignment class has everythign it needs to operate successfully.

make.assignment.class returns a list of elements with class highway.assignment.class suitable for building a assignment.set. The specific list elements are:

name: A unique name for the class, constructed according to the rules of legal names for R symbols; see make.names for help in creating a good name
demand: A demand matrix with demand for this class (e.g. trucks, or high-occupancy vehicles)
network.set: The network topology, including turn penalties and open links, for this assignment class
cost.function: A class-specific cost function; only called if specifically coded in the assignment set cost function