# Table Pad Define Dialog Operations

To enter the Define dialog for a Table Pad, double-click anywhere within the confines of the page (except on a variable name or on the title bar). Or, with the pad active choose Define Table from the Map/Model menu. The Table Pad Define dialog is shown in Figure 6-64. Define dialog operations are described in the text which follows.

Loading/Removing/Exchanging Variables: The two lists at the top of the dialog, along with the buttons between the lists, are used to load, remove, and exchange the variables to be displayed in the Table Pad page. All model variables (stocks, flows, converters) will appear in the Allowable list. Variables to be plotted appear in the Selected list. When a variable has been loaded to the Selected list, it will appear gray in the Allowable list. Here's how to move variables between the two lists.

- Loading Variables: To load a variable to the Selected list, double-click the variable name in the Allowable list. Or, select it, and then click the >> button. To select multiple variables, simply drag-select or shift-click to move adjacent variables, or control-click (Windows) or command-click (Macintosh) to move noncontiguous variables.

Figure 6-64 Table Pad Dialog

Helpful Hint: If a variable is selected within the Selected list, any variables that you load to the Selected list will be placed above the selected variable.

- Removing Variables: To remove a variable from the Selected list, double-click the variable name. Or select it and click on the << button between the two lists. To select multiple variables, simply drag-select or shift-click to move adjacent variables, or control-click (Windows) or command-click (Macintosh) to move noncontiguous variables.

- Exchanging Variables: To exchange one or more variables in the Allowable list for one or more variables in the Selected list, select the desired variable(s) in each list. Then, click on the <-> button. The variables will be exchanged.

Helpful Hint: As you load variables to Table Pad pages, note the words "Blank Line" at the top of the Allowable list. You may enter as many Blank Lines (to separate variables for formatting purposes) between variables as you'd like.

Setting the Table Type: Below the Allowable list, you'll a find a check box entitled "Comparative." When you check the Comparative box, the page will maintain a cumulative record of the results for one variable, from each of a series of consecutive simulations, rather than displaying anew the results of each simulation. When a comparative table is generated in conjunction with Sensitivity Analysis, a "?" will appear in the top-right corner of the page. A click on the "?" will pop up a journal of the most recent sensitivity setup used to create the page. This process was illustrated in Figure 6-63.

Helpful Hint: To clear comparative data, click on the Dynamite icon in the upper right-hand corner of the Table or position the Dynamite tool within the confines of the numerical display portion of the page, then click. See Chapter 5 for details on this use of the Dynamite.

Setting the Table Orientation: The Orientation check box gives you the option of arraying your table output in vertical columns or in horizontal rows.

Titling a Page: To title a specific page of the Table Pad, select the text in the Title field of the Table Pad dialog. Then, type the desired title. The title will appear in the title bar of unpinned Pads. It also will appear with the Pad name and page number at the top of the page. Note that titles will be printed at the bottom of the Table when you print a Table Pad.

Adding Pages: Above the OK button is the apparatus for adding pages to a Table Pad. Once you have loaded variables into the Selected list of the first page of a Pad, the up-arrow in the apparatus will become active. Click on the arrow (next to the word "New") to create a new page. You can add as many pages to a Pad as you'd like. You can click on the up or down-arrows to move between pages from within the dialog. Or, you can click on the page-turn buttons on the Table Pad surface.

Setting the Report Interval: The Report interval determines at what interval the software will report numerical values on the table during a simulation. You can use the Report interval box to set the Report interval to any value greater than or equal to DT, and less than or equal to the time at which you've specified your simulation to end. In addition, you can check the Every DT box to cause the software to report numerical values each time a round of calculations is made. Such a setting is a good choice when debugging your model, because you can see the results of the calculations, as the calculations are made. If you subsequently un-check Every DT, the Report interval box will reappear. Report interval is global. It applies to all pages in all Table Pads.

Use Month Names: When "Months" is selected as the unit of time in the Run Specs... dialog, the Use Month Names check box becomes available to you. Check the box to cause time headings in the table to be displayed textually as month names rather than numerically. The software will map time 1 to the month January, time 2 to February, etc.

Reporting Beginning vs. Ending Balances: There are several options for, and issues associated with, reporting numerical values in Tables. To illustrate these options and issues, we'll make use of the simple system shown in Figure 6-65. The system consists of Population, births, deaths, and net growth. You may wish to construct the model, to work through these issues.

Figure 6-65 Simple Population Model

In choosing whether to report Beginning or Ending balances, the issue has to do with when the values of stocks and converters are displayed, relative to the time at which flow values are displayed. The issue arises because of an ambiguity in the use of numbers to reflect points in time. For example, when you receive an Annual Report dated 1992, it is understood that this means "for the year 1992." However, as a number, 1992 means 1992.0. 1992, as used in "for the year 1992" really means 1992.999... (i.e., it's the end of the year 1992). Although the spoken language glosses over this ambiguity, computers can't! They need to know: do you mean end of 1992 or beginning of 1992?

The software allows for either interpretation. The Ending balances option will attach values for all stocks, flows, and converters to the end of each report interval. If you opt for Beginning balances, values will be attached to the beginning of each report interval. Whichever Beginning/Ending Balances choice you choose will apply to all pages of all Table Pads.

We'll use the model outlined in Figure 6-65 to illustrate the differences between Beginning and Ending Balances reporting. The results displayed in Figure 6-66 show values for Population (the stock) under both Beginning and Ending Balances options. First, note that under the Ending balances option there is no Month 2.0. Instead, there is "end of time period 1." The value for Population at "1:end" corresponds exactly with the value for Population at 2.00. Note also that when the Ending Balances option is in effect, an "initial" value is displayed for Population. This is the value the stock takes on at the very outset of the simulation. It's the same value that's displayed for Time 1.00 in the Beginning Balances case. Likewise, a "Final" value appears in the Beginning Balances case.

Figure 6-66 Ending vs. Beginning Balances - Summed Reporting of Flows

One other thing occurs when the Ending Balances option is in effect. Flow values are reported out one report interval later than where they appear when Beginning Balances is in effect. The shift in the reporting of flow values is suggested in Figure 6-66, and illustrated clearly in Figure 6-67 where deaths is defined with a step increase at time 2.0.

Figure 6-67 Shifting of Flow Value Display

The step increase in deaths raises it up to equal births. Note that the step-increase is displayed at the end of the first DT of Month 2 (i.e., Month 2:.25) in the Ending balances case, and at Month 2.00, which is one DT earlier, in the Beginning balances case. In the Beginning balances case, births are equal to deaths at Month 2.0. Yet the value of the stock has incremented from 103 to 104. In the Ending balances case, the step-increase is displayed at the end of the first DT of Month 2. This is the value of the flow which prevailed over the interval from the last DT of Month 1 to the end of the first DT of Month 2. The stock therefore is not incremented during the first DT of Month 2.

You'll have to decide which display option makes most sense for your particular simulation. In general, when you are working with financial variables which often are reported in end-of-time-interval fashion, it probably makes most sense to use the Ending balances option.

Reporting Instantaneous vs. Summed Flows: The next issue associated with the display of numerical values in Tables is with respect to flows. Should you report them as instantaneous values, or should you sum them over the report interval? The option you choose applies to all pages of all Table Pads. When summed reporting is in effect, the values for flows are displayed as the amount which actually increments (or decrements) the stock over the Report interval you have specified. In Summed mode, with a report interval larger than DT, the flow values that are displayed will be the sum of the flow values that would have been displayed for each DT during the Report interval. To illustrate, shown in Figure 6-68 are values for births and deaths displayed in Summed mode, first with a Report interval of DT, and then with a Report interval of 1 (Ending balances is in effect).

Figure 6-68 Comparing Summed Values for Flows with Differing Report Intervals

With a Report interval equal to DT, births - which are defined as equal to a constant 8 per month - appear as a constant 2 per DT (since DT = 0.25 and there are 4 DT's in a month). Similarly, deaths - defined as equal to a constant 4 per month - are reported as a constant 1 per DT. The net of births over deaths therefore is 1 per DT, which is exactly the amount by which the stock (Population) is incremented per DT. In the second Table, the Report interval is set to 1.0. This means that the flow values are cumulated over 1 month (or 4 DTs). Flow values do not usually remain constant from DT to DT, as they do in this illustration. Hence, the cumulative value displayed for flows usually will not be equal to (1/DT) times the flow value in the first DT of a time unit.

It is also possible to display the instantaneous values of flows. When you use Instantaneous reporting, the actual calculated flow value, as determined from the flow's equation logic, is displayed. In Figure 6-69, for example, during each DT the births flow is reported as 8. The deaths flow is reported as 4. The difference between the two is 4. Yet Population increases by only 1 in each DT. This is due to the fact that before the net difference between births and deaths is added to the previous value of Population to produce a new value for Population, the difference is multiplied by DT (for this illustration, DT is set to 0.25). When reporting flow values in the instantaneous mode, this multiplication is not considered (for display purposes). Obviously, however, it is being considered when making the calculation to update the value of the stock.

Figure 6-69 Instantaneous Reporting of Flows -- Ending Balances, Report Interval = DT

Using the C -> F Button: Located below the Selected list in the Table Pad define dialog, the C -> F button allows you to make converters act like flows in their Table Pad display. The issue arises because, for Table display purposes, converters are not always treated in the same way as flows. The default is to report converters as instantaneous values. When you are reporting flows as Summed, there can be a mismatch between the reporting of a flow value, and the reporting of a converter value which depends upon that flow.

For example, as the left panel of Figure 6-70 illustrates, the value displayed for net growth (a converter) is not equal to the difference between the displayed values for births and deaths (both flows). This is because net growth is being considered to be a converter (for display purposes), and hence its instantaneous value is being displayed. [If you have been building this example as we have progressed you will notice the software automatically C->F'd net growth. Any converter defined by flows is automatically C->F'd on tables.]

When net growth is C -> F'd, you obtain the values displayed in the Table (shown in the right panel of Figure 6-70) - which are the values you'd expect.

Figure 6-70 Displaying Converter Values without and with C --> F -- Ending Balances, Summed Reporting of Flows

Whenever a converter is a function of one or more flows (but no stocks, or other converters) - and unless that converter is a graphical function - it will be automatically C -> F'd upon entry into the Selected list in the Table dialog. You may of course override this automatic conversion. To do so, select the converter, then click the button labeled C <- F (the arrow is now reversed) which appears below the Selected list in the dialog. You also may C -> F any converter you choose simply by selecting it and then clicking once on the C -> F button. Whenever a converter has been C -> F'd, an "*" will appear to the left of the converter's name in the Selected list.

Note that the C -> F operation is local to the Table Pad page you are defining. In general, if you have converters that are playing the role of flow concepts in your model, make sure that they are using the C -> F option! If you are getting what you consider to be "strange" numerical results displayed in your Tables for converters, you should check to see if these converters really should be treated as flows (for display purposes). If they should, C -> F them. But then remember that you have done it! The "*" in front of the variable's name should help to jog your memory.