.set_default_parameters+

BPR link performance function method

Description

This .set_default_parameters allows you to set the BPR function’s default parameters in various ways:

  1. Define defaults for all link segments,
  2. Define defaults for all link segments of a particular mode,
  3. Define defaults for all link segments of a particular mode and link segment type

In case 3) is not available, PLANit will see if 2) is available. If 2) is not available, PLANit will see if 1) is available. If 1) is also not available, PLANit will utilise the pre-set defaults.

Signature

.set_default_parameters(alpha, beta, mode_xml_id=None, link_segment_type_xml_id=None)

with

Parameter Type Unit Compulsory Description
alpha float None YES Alpha parameter of BPR function
beta float None YES Beta parameter of BPR function
mode_xml_id string None NO* Mode (XML) id to relate parameter to
link_segment_type_xml_id string None NO Link Segment Type (XML) id to relate parameter to

* mode_xml_id becomes compulsory when link_segment_type_xml_id is provided

Return type

None

Example 1

Set only network wide defaults

from planit import *

# prep
planit_instance = Planit()
planit_instance.project.set(TrafficAssignment.TRADITIONAL_STATIC)

# set physical cost to BPR link performance function
planit_instance.project.assignment.set(PhysicalCost.BPR)

# override the default alpha and beta
alpha = 0.87
beta = 5
planit_instance.project.assignment.physical_cost.set_default_parameters(alpha, beta)

Example 2

Set network wide defaults for a mode with XML id “1”

from planit import *

# prep
planit_instance = Planit()
planit_instance.project.set(TrafficAssignment.TRADITIONAL_STATIC)

# set physical cost to BPR link performance function
planit_instance.project.assignment.set(PhysicalCost.BPR)

# override the default alpha and beta
alpha = 0.87
beta = 5
planit_instance.project.assignment.physical_cost.set_default_parameters(alpha, beta, "1")

Example 3

Set default parameters for mode (XML) id “1” and link segment type (XML) id “4”

from planit import *

# prep
planit_instance = Planit()
planit_instance.set(TrafficAssignment.TRADITIONAL_STATIC)

# set physical cost to BPR link performance function
planit_instance.project.assignment.set(PhysicalCost.BPR)

# override the default alpha and beta
alpha = 0.87
beta = 5
planit_instance.project.assignment.physical_cost.set_default_parameters(alpha, beta, "1", "4")

See also

N/A

Source code

Class BPRCostWrapper in projectwrappers.py

Last modified January 1, 0001