Constraint Entry Style

Figure 1 - Constraints Command Buttons

There are three constraint Entry Styles - One-Sided, Two-Sided, and Formula. The Entry Style button (Figure 1, right) at the bottom of the Constraint Settings window selects the style of constraint being created. The styles are:

  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.

One-Sided and Two-Sided styles allow constraints to be entered using logical operators - < (less than), <= (less than or equal to), > (greater than), >= (greater than or equal to) or = (equals).

A Formula constraint, on the other hand, allows a constraint to use any valid Excel formula. For example, the formula '=IF(A1>100, B1>0, B1<0)' could be entered. This constraint requires the value in cell B1 to be positive or negative depending on the value in cell A1.

In general, entering constraints in the One-Sided or Two-Sided style helps Evolver find the optimal solution faster. The formula just discussed above could be entered in cell D1 as =IF(A1>100, B1, -B1).  Then a simple One-Sided constraint can be added, requiring that D1>0, achieving the same result without using a Formula constraint style.