Chapter 2

A Sample Problem

Introduction

In this chapter we will run through a sample problem from beginning to end in order to demonstrate how to use the package. While not all problems or modules are identical there is enough similarity that seeing one example will make it very easy to use any module in this software. As we mentioned in the introduction, the first instruction is to select a module to begin the work.

In the accompanying figure we display the modules as they are listed when you use the MODULE tool on the utility bar (as opposed to the Module option in the main menu at the top). As you can see, there is a total of 30 modules available. They are divided into three groups. The first group is typically relevant to all POM and QM books, while the second group typically appears only in POM books and the third group appears only in QM texts.

If you choose the Module option from the Main Menu, you get the same modules listed in a single list in alphabetical order.

Creating a New Problem

Generally, the first menu option that will be chosen is File, followed by either New to create a new data set or Open to load a previously saved data set. In the figure that follows we show the creation screen that is used when a new problem is started. Obviously, this is an option that will be chosen very often. The creation screens are similar for all modules but there are slight differences that you will see from module to module.

The top line contains a text box into which the title of the problem can be entered. The default title for problems is initially '<untitled>'. The default title can be changed by pressing the button [Modify Default Title]. For example, if you change the default title to 'Homework problem' then every time you start a new problem the title will appear as Homework problem and you would simply need to add the problem number to complete the title. If you want to change the title after creating the problem, this can easily be done by using the Format, Title option from the main menu bar or from the toolbar .

For many modules it is necessary to enter the number of rows in the problem. Rows will have different names depending on the module. For example, in linear programming, rows are 'constraints', while in forecasting, rows are 'past periods'. At any rate, the number of rows can be chosen with either the scroll bar or the text box. As is usually the case in Windows they are connected. As you move the scroll bar, the number in the text box changes; as you change the text, the scroll bar moves. In general, the maximum number of rows in any module is 90. There are three ways to add or delete rows or columns after the problem has been created. You may use the options in the File menu, you may right click on the data table and this will bring up both copy and insert/delete options or to insert a row or insert a column you may use the tools on the toolbar .

This program has the capability to allow you different options for the default row names. Select one of the six option buttons in order to indicate which style of default naming should be used. In most modules the row names are not used for computations but you should be careful because in some modules (most notably Project management and MRP) the names might be relevant to the computations. In most modules the row names can be changed by editing the data table.

Many modules require the number of columns. This is given in the same way as the number of rows. The program gives you a choice of default values for column names in the same fashion as row names but on the tab named Column names.

Some modules, such as the one shown, will have an extra option box, such as for choosing minimize or maximize or selecting whether distances are symmetric or not. Select one of these options. In most cases this option can be changed later on the data screen.

When you are satisfied with your choices, click on the [OK] button. At this point a blank data screen will appear as given in the following figure. Screens will differ module by module but they will all resemble this screen below.

The Data Screen

The data screen was described briefly in Chapter 1. It has a data table and for many models there are extra data that appear above the data table as shown below.

Entering and Editing Data

After a new data set has been created or an existing one has been loaded the data can be entered or edited. Every entry is in a row and column position. You navigate through the spreadsheet using the cursor movement keys (or the mouse). These keys function in a regular way with one very useful exception - the [Enter] key.

The [Enter] key takes you to the next cell in the table, first moving to the right and then moving down. When a row is finished, the [Enter] key goes to the first cell in the next row that contains data rather than a row name. For example, in the screen below, if you are at the end of the row named 'Constraint 1' and you press [Enter] then the cursor will move to the cell with a '0' in the next row. It is possible to set the cursor to go to the first cell, the one with the name in it, by using Help, User information.

In addition, if you use this key to enter the data, after you are done with the last cell the program will automatically solve the problem (saving you the trouble of clicking on the SOLVE tool). This behavior can be adjusted by using Help, User information and in addition if you want the program to automatically save the file when you are done entering data then this too can be accomplished through Help, User information.

The instruction frame on the screen will contain a brief instruction describing what is to be done. There are essentially three types of cells in the data table.

One type is a regular data cell into which you enter either a name or a number. When entering names and numbers, simply type the name or number; then press the [Enter] key or one of the direction keys or click on another cell. If you type an illegal character, a message box will be displayed indicating so.

A second type is a cell that cannot be changed.

A third type is a cell that contains a drop-down box. For example, the signs in a linear programming constraint are chosen from this type of box, as shown in the following illustration. To see all of the options, press the arrow on the dropdown box.

When you are finished entering the data, press the SOLVE tool on the toolbar or use [ F9 ] or File, Solve and a solution screen will appear as given in the following illustration. The original data is in black and the solution is in a color. Of course, these are only the default values as all colors may be set by using Format, Colors .

The Solution Screen

An important thing to notice is that there is more solution information available than the one table displayed. This can be seen by the icons given at the bottom. Click on these to view the information. Alternatively, notice that the Window option in the main menu is now enabled. (This is shown in the next figure.) It is enabled at the first solution display unless you reset this option by using Help, User information.

Now that we have examined the creation and solution of a problem, we explain all of the options that are available in the Main Menu.