Parameters of Equilibrium assignment

Equilibrium assignment: Basis tab

On this tab, enter the basic parameters for the procedure.

Element	Description
Use current assignment result as initial solution	If this option is checked, the assignment will use existing paths and volumes of the previous assignment as an initial solution. Notes This option is recommended in the case of modified demand (e.g. due to 'Read matrix additionally' or matrix editing in the matrix editor). First, the former assignment result is scaled according to the new demand and then the assignment continues to calculate the new result. Usually, this requires fewer iterations than a complete recalculation. In this way, a lot of computation time can be saved in models with feedback from the assignment calculation to the demand calculation. Multiple network modifications and repeated use of this option result in a different assignment result than a new assignment without this option would have resulted in, since there are numerous states which satisfy Wardrop's first principle of the equilibrium procedure. If this option is not selected, the initial solution is calculated using incremental assignment (Incremental assignment (static)). For this initial solution calculation, the demand portion defined in the section Calculate initial solution: Incremental assignment is used for each iteration step. Note These settings are also regarded if an existing assignment result is to be used as an initial solution, but no assignment result can be found.
Initial solution calculation by incremental assignment	OD demand share per iteration step Incremental assignment assigns the user-defined percentage of demand per iteration step (Parameters of incremental assignment). Notes This setting applies in two cases: The option Use current assignment result as initial solution has not been selected. The option Use current assignment result as initial solution has been selected, but an assignment result could not be found.
Network balancing	Permitted deviation of impedances of alternative routes Absolute deviation The absolute difference of impedances between coupled equalization of routes. The procedure terminates as soon as the value falls below. Relative deviation The proportional difference of impedances between coupled equalization of routes. The procedure terminates as soon as the value falls below. Maximum number of iterations Via this button, you can set the number of internal balancing iterations. The number may vary due to the fact, which of the external iterations is currently being calculated. This is why you can assign the steps of external iterations to classes (Setting the number of balancing iterations). Notes It might make sense to calculate a lower number of internal balancing iterations in the first external iterations. The button label shows the current settings in brief. By default, no classes have been defined, thus, the number of balancing iterations is the same for all external iterations. When reading older versions or procedure parameter files, a class with a constant number of internal balancing iterations is defined.

Equilibrium assignment: Convergence criteria tab

Element	Description
Use classical convergence criteria	If this option is selected, the classical criteria described below are taken into account.
Use extended convergence criteria	If the option is selected, you can define additional termination conditions in addition to the classic convergence criteria. These are described further down in the table in the Extended section. The extended criteria can be used to check which links and turns show greater deviations in volume and/or impedance between iterations, and a minimum percentage of converged links and turns can be used as an additional convergence criterion (Fundamentals: Convergence criteria of assignment quality). Note The shares of network objects based on the extended convergence criteria are always calculated, regardless of the option set, and output in the PrT assignment quality data list.
Termination conditions	Maximum number of iterations Specify the maximum number of iterations after which the procedure ends if no convergence occurs. Maximum gap Measure of the difference between the current loaded state and the balanced state. The procedure terminates as soon as the value falls below.
Classical	Convergence statistics The settings you make here only take effect for the output of the shares in the PrT assignment quality data list. Relative difference between previous and current iteration Enter the desired value for the relative difference for link volume/impedance and turn volume/impedance for comparing results of successive iterations. The input values for links apply to the output of the shares of the connectors. Ignore links and turns with a volume < Network objects whose volume is beneath the defined threshold are not taken into account.
Extended	Relative difference between previous and current iteration For the comparison of results of successive iterations, a value for the relative difference must be defined for each convergence criterion. The calculation of the share of objects is based on the links or turns/main turns open in the network. Link volume <=/Link impedance <= Enter a numerical value and define the share of links in percent that meet the respective condition. Turn volume <=/Turn impedance <= Enter a numerical value and define the share of turns in percent that meet the respective condition. Note The input value for the share applies to both the turn and the main turn together. Ignore links and turns with a volume < Network objects whose volume is beneath the defined threshold are not taken into account. Consider only active links and turns If the option is selected, the termination is based on the relative differences for the active links, turns, and main turns. Number of iterations taken into account for convergence Enter the number of iterations to be taken into account. Notes The assignment is considered converged if the condition for link volume or link impedance, the condition for turn volume or turn impedance, and the condition for the gap are fulfilled. Besides, these criteria must be fulfilled in the specified number of consecutive iterations. The convergence attributes of the assignment are always stored at links, turns, main turns, and connectors.

Setting the number of balancing iterations

1. Make sure the Parameters: Equilibrium assignment window is open (Parameters of Equilibrium assignment).

2. Click the button next to Maximum number of iterations.

The window Maximum number of balancing iterations opens. When opened for the first time, the list contains a single entry.

Element	Description
External iteration	Classification of the iteration steps of the external iteration in classes Notes Double-click in the selected cell to edit the value. You cannot change the highest class limit. For an existing assignment, you can enter the value 0 to adjust only the path volumes.
Number of balancing iterations	Number of internal iterations for balancing route volumes Note Double-click in the selected cell to edit the value.
Create	Use this button to create additional classes. Notes The new class will automatically be created after the currently selected class. The class limit of the new class is automatically placed between the two adjacent class limits. If you add classes at the upper limit, the highest value is automatically increased. Double-click in the selected cell to edit the value. You cannot change the highest class limit.
Delete	Use this button to delete the currently selected row.

3. Confirm with OK.

The number of balancing iterations has been set for the defined classes of external iterations.