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Exhibit 9.4 Constraint entry for X 1
manually. Imagine that we are beginning the process of entering the two types of
constraints in our formulation. The first is the maximum number of project types
that can be selected in a quarter. By selecting the Add button in the constraint area of
the dialogue box, the Add Constraint dialogue entry box appears. Exhibit 9.4 shows
the entry of X 1
25. The Cell Reference entry is represented by the changing cell
that contains the value for the project type 1 units selected, D2, and the Constraint
is the RHS of the constraint, B2 (25). Rather than enter 25 in the Constraint area,
I have provided a cell location, B2. This will permit you to simply change the cell
location value at any time, and the constraint will be automatically updated to the
new value when Solver is executed.
The entry of the resource hour constraints is a more complex task. Above we
noted that cells A23:D23 are the summation of the products of the decision vari-
ables and hours consumed by the use of each project type. Thus, each of these four
sums represents the use of each resource hour type due to the selected number of
projects. We will use these cells, A23:D23, as the Cell Reference entries and the
corresponding RHS entries ( Constraint ) are found in A22:D22. In Exhibit 9.3 you
can see the first entry (A23 <
A22) represents the constraint for resource A. The
creation of the formula in A23 greatly simplifies data entry. Yet, it is possible to
enter the constraints directly into the Constraint section of the Add Constraint dia-
logue box. We would do so by typing the same formula that appears in cell A23
and then entering the RHS, A22, in the Cell Reference . Note that you will have to
change the sense of the inequality between these quantities to >
to preserve the
proper inequality of the constraint.
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