MicrosoftВ® Office ExcelВ® 2007: Data Analysis and Business Modeling (Bpg -- Other)

Overview

• How can a large drug company determine the monthly product mix at their Indianapolis plant that maximizes corporate profitability?

• If Microsoft produces Xbox consoles at three different locations, how can they minimize the cost of meeting demand for them?

• What price for Xbox consoles and games will maximize Microsoft’s profit from Xbox sales?

• Microsoft would like to undertake 20 strategic initiatives that will tie up money and skilled programmers for the next five years. They do not have enough resources for all 20 projects; which ones should they undertake?

• How do bookmakers find the best set of “ratings” for NFL teams, in order to set accurate point spreads?

• How should I allocate my retirement portfolio among high-tech stocks, value stocks, bonds, cash, and gold?

In all these situations, we want to find the best way to do something. More formally, we want to find the values of certain cells in a worksheet that optimize (maximize or minimize) a certain objective. Microsoft Office Excel Solver tool helps you answer optimization problems.

An optimization model has three parts: the target cell, the changing cells, and the constraints. The target cell represents the objective or goal. We want to either minimize or maximize the amount in the target cell. In the example of a drug company’s product mix given above, the plant manager would presumably want to maximize the profitability of the plant during each month. The cell that measures profitability would be the target cell. The target cells for each situation described at the beginning of the chapter are listed in Table 26-1 on the next page. Keep in mind, however, that in some situations you might have multiple target cells. For example, Microsoft might have a secondary goal to maximize Xbox market share.

Changing cells are the worksheet cells that we can change or adjust to optimize the target cell. In the drug company example, the plant manager can adjust the amount produced for each product during a month. The cells in which these amounts are recorded are the changing cells in this model. Table 26-2 lists the appropriate changing cell definitions for the models described at the beginning of the chapter.

The best way to understand how to use Solver is by looking at some detailed examples. In later chapters, you’ll learn how to use Solver to address each of the problems presented in this chapter, as well as several other important business problems.

To install Solver, click the Microsoft Office Button, click Excel Options, and click Add-Ins. In the Manage box at the bottom of the window, select Excel Add-ins, and click Go. Check the Solver Add-in box in the Add-Ins dialog box, and click OK. After Solver is installed, you can run Solver by clicking Solver in the Analysis group on the Data tab. Figure 26-1 shows the Solver Parameters dialog box. In the next few chapters, you’ll see how to use this dialog box to input the target cell, changing cells, and constraints for a Solver model.

Figure 26-1: The Solver Parameters dialog box

After you have input the target cell, changing cells, and constraints, what does Solver do? To answer this question, you need some background in Solver terminology. Any specification of the changing cells that satisfies the model’s constraints is known as a feasible solution. For instance, in our example, any product mix that satisfies the following three conditions would be a feasible solution:

• Does not use more raw material or labor than is available.

• Does not produce more of each product than is demanded.

• Does not produce a negative amount of any product.

Essentially, Solver searches all feasible solutions and finds the one that has the “best” target cell value (the largest value for maximum optimization, the smallest for minimum optimization). Such a solution is called an optimal solution. As you’ll see in Chapter 27, “Using Solver to Determine the Optimal Product Mix,” some Solver models have no optimal solution and some have a unique solution. Other Solver models have multiple (actually, an infinite number of) optimal solutions. In the next chapter, we’ll begin our study of Solver examples by examining the drug company product mix problem.