Phases
The Public Transport program executes its main processes—data processing and modeling—within a series of phases. You control all the phases and can initiate additional, context-sensitive computations within them. The phases, presented in the order they would normally be implemented, are:
-
NODEREAD — Computes node based variables.
-
LINKREAD — Computes link based variables.
-
DATAPREP — Prepares the public transport network for modeling.
-
MATI — Computes trips for loading.
-
SKIMIJ — Extracts skims and select link results, saving them, generally in working matrices.
-
MATO — Manipulates and reports skim, select-link, and loading-analyses matrices.
The NODEREAD, LINKREAD, MATI, and MATO phases provide data manipulation facilities, and are secondary to the main functions of the Public Transport program. They are optional.
You specify the exact configuration for the Public Transport program to run through a combination of phases and control statements.
Control statements provide information and instructions to the program. In the Public Transport program, control statements are either static or dynamic. Static statements may be present anywhere in the job stream; the program evaluates them once. Dynamic statements may be present only within phases; the program evaluates them as encountered, during the execution of the phases.
Only context-sensitive dynamic control statements are available to the phases; a list of valid statements is provided with the description of each phase. See Control Statements for more information. You only must code phases that contain control statements; you need not code empty or null phases. Specify phases in a script as follows:
PHASE=DATAPREP ;Generate access/egress legs GENERATE ... ... ;End of GENERATE ENDPHASE
Regardless of the functionality selected for any run of the Public Transport program, a requirement is that a network, basic or public transport, is always input. This is read and set up at the start of each run; no user intervention is required.
A diagram showing how the phases would be used in a typical public transport model follows:
In the NODEREAD phase, you can compute node-based information from the input network’s node attributes with NETI. This information is for use primarily in the DATAPREP phase but is available in later phases if the DATAPREP phase is active.
The control statements within the NODEREAD phase are executed once per node. Only one NODEREAD phase is permitted per run.
The computed variables may be scalars or vectored by node. The use of a vectored variable produces an array containing a computed value for each node. Vectored variables have the case insensitive prefix "nw".
The evaluated expression may contain any valid variables, numeric or string, and node based variables from the input network. Input node variable names must have the case insensitive prefix "ni".
An example of a computed node variable is:
NW.XplusY = NI.X+NI.Y
Computed variables are available for the duration of the run but not saved back to the network.
See Example 2: Preparing a public transport network from TRIPS link data for an example of this phase.
Control statements available in this phase
Public Transport variables available in this phase
In the LINKREAD phase, you can compute link-based information from the input network’s link attributes with NETI. This information is for use primarily in the DATAPREP phase but is available in later phases if the DATAPREP phase is active.
The control statements within the LINKREAD phase are executed once per link. Only one LINKREAD phase is permitted per run.
The computed variables may be scalars or vectored by link. The use of a vectored variable produces an array containing a computed value for each link. Vectored variables have the case insensitive prefix "lw".
The evaluated expression may contain any valid variables, numeric or string, and node based variables from the input network. Input link variable names must have the case insensitive prefix "li".
An example of a computed link variable is:
LW.GCTime=LI.Time*1.5
Computed variables are available for the duration of the run but not saved back to the network.
See Example 2: Preparing a public transport network from TRIPS link data for an example of this phase.
Control statements available in this phase
Public Transport variables available in this phase
The DATAPREP phase invokes the Public Transport network development process and provides the mechanism for generating and/or reading nontransit legs.
You can develop nontransit legs with one or more GENERATE control statements, or you can produce them externally to the Public Transport program and input them in this phase.
You can compute data for nontransit leg generation from the input network with the COMP statement.
See Public transport network development for examples of this phase.
Control statements available in this phase
Public Transport variables available in this phase
The MATI phase produces working matrices, (MW[#]), from FILEIMATI matrices (MI.#.name), although COMP statements can also compute working matrices.
The MATI phase is executed for each origin zone, I, before the route evaluation, skimming, loading, and loading analyses processes are done for each zone pair, I-J.
This phase provides a flexible mechanism for generating and manipulating one row of a matrix at a time. You might use this phase to:
-
Examine the matrix input with FILEI MATI, one row at a time, and determine if there is anything specific about zone I that could affect further processing for that zone. For example, if MATI points to a highway network matrix, and the matrix indicates that there is no highway access for zone I, you might set a variable for zone I and test in the SELECTIJ phase.
-
Compute a row of trips, from an origin zone (I) to all zones (J), using the COMP statement and the built-in ROW functions, and save the trips in a working matrix, MW[#], for subsequent loading. You can also do this in the SELECTIJ phase, but for a zone pair at a time. The working matrix is designated for loading with PARAMETERS TRIPSIJ[userclass].
-
Input matrices external to the Public Transport program with FILEI MATI, and then manipulate, report, and save those matrices with FILEI MATO. You can merge highway skims with skims extracted in the Public Transport program run.
The working matrix may be reported with the PRINTROW statement. With the BREAK statement, you can use the MATI phase to select zones for processing.
See Public transport loading for an example of this phase.
Control statements available in this phase
Public Transport variables available in this phase
The SELECTIJ phase selects pairs of zones, I-J, for bypassing the route-evaluation process.
The ROUTEI and ROUTEO subkeywords I, J, and SELECTBYMAT provide the first line of selection but they do not control specific I-J combinations. The SELECTIJ phase allows a finer selection of specific I-J combinations, although if the I-J combination is precluded by the values on the ROUTEI and ROUTEO, that I-J pair is not available to this phase.
The Public Transport program executes the SELECTIJ phase prior to the route-evaluation process for the I-J pair. (Route evaluation is a time consuming process, therefore judicious use of this phase can have a significant impact on overall processing time.)
Only zone pairs for evaluated routes are available for the skimming, loading, and loading analyses processes.
This phase can compute the trips to be loaded for each I-J pair. For example:
PHASE=SELECTIJ if(I < 10) CONTINUE if(J > 10) BREAK TRIPSIJ=MI.1.1 * 0.75 PRINT LIST=I,J,TRIPSIJ ENDPHASE
In this fragment of code, the I-J pairs loaded range from I=10-ZONES to J=1-9. The trips to be loaded are computed from the input trip matrix and reported.
Control statements available in this phase
Public Transport variables available in this phase
The SKIMIJ phase extracts skims and select-link outputs with special functions described in "Select-link functions", then saves them, generally in working matrices with the COMP MW[#] statement.
The Public Transport program invokes SKIMIJ for each zone pair, I-J, immediately after route evaluation.
See Public transport skimming for an example of this phase.
In the MATO phase, the Public Transport program revises, combines, reports and writes work matrices to the FILEO MATO files.
The program executes this phase once for each origin zone, I, after completing the route evaluation, skimming, loading, and loading analyses processes for all destination zones of that origin zone.
Generally, you use the MATO phase with the matrices produced by the skimming and loading analyses phases, but you can also process other working matrices similarly.
You can manipulate matrices with the COMP statement and a set of built-in ROW functions, and create a report with the PRINTROW statement. With the BREAK statement, you can use the MATO phase to select zones for processing.
See Public transport skimming for an example of this phase.
Control statements available in this phase
Public Transport variables available in this phase