Constraints

Figure 1 - Constraints Panel

Evolver models can include constraints, or conditions that must be satisfied for a solution to be valid. Constraints are shown in the Constraints table (Figure 1, right) at the bottom of the Model Definition dialog.

The Constraints table consists of four columns: 

  • Check box - Each constraint has a check box to its left. Activate or deactivate any (or all) of the current constraints by checking or unchecking its box.

  • Deactivating a constraint will remove it from the optimization, but will not delete it!

  • Description - The constraint description. See Constraint Entry Style for more information.
  • Formula - The constraint formula. See Constraint Entry Style for more information.
  • Type - The constraint type - Hard or Soft. See Constraint Types for more information.

Figure 2 - Constraint Settings Window

To add a constraint, click the Add button. This will open the Constraint Settings window (Figure 2, right), where the constraint can be configured. See Configuring a Constraint, below, for more information.

To edit an existing constraint, select the constraint by clicking inside its row (not the check box to the left) and click the Edit button.

To delete an existing constraint, select the constraint by clicking inside its row (not the check box to the left) and click the Delete button.

Configuring a Constraint

There are three constraint Entry Styles:

  1. One-Sided - The acceptable adjustable cell values must exist above or below the Constraining Value(s).
  2. Two-Sided - The acceptable adjustable cell values must exist between the Constraining Value(s).
  3. Formula - The acceptable adjustable cell values must exist within a set of values as determined by a formula.

To select the type of constraint, use the Entry Style button at the bottom of the Constraint Settings window (Figure 2, above). See Constraint Entry Style for more information.

The most basic constraint is a One-Sided Constraint, shown in Figure 2, above; the entries for this constraint are:

  • Range to Constrain - The cell(s) in Excel for which values will be constrained during the optimization.
  • Operator - the comparison operator (greater than, less than, etc.) to determine on which side of the Constraining Values acceptable results exist.
  • Constraining Values - The values to which the adjustable cells should be limited.

Figure 3 - Constraints Panel

For more detailed configurations, click the More button. This will expand the window to show all options (Figure 3, right). The following fields are available:

  • Description - The description of the constraint. This value will display in the Description column of the Contstraint table (above).
  • Constraint Type - Select Hard or Soft constraint. See Constraint Types for more information.
  • Options - Each constraint type includes specific options that can be set. See Constraint Types for more information.
  • Summary - A basic summary of the constraint as configured.