Page 58 - ExtendSim User Guide
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Building a Model
Working with block dialogs
Combining the sources
The Math block combines the values from the two water sources. As indicated by the plus sign on its icon when you placed the block in the model, the Math block is set by default to add its inputs. There is no need to change its dia- log settings.
☞ Although you don’t need to for this model, the Math block function can be changed directly in its dialog or by right- clicking a special area on its icon. For the Math, Decision, and Simulation Variable blocks (Value library), the icon’s lower right corner has a sensitized area that looks like a partially turned page. You can right-click that area to change dialog settings.
Water in the reservoir
The Holding Tank block represents the level of water in the reservoir. In this model, the Hold- ing Tank has no beginning contents and does not release any of its contents.
Open the Holding Tank block’s dialog. In the dialog, set:
Initial contents: 0 (Default)
Inputs are: integrated (delay)
Enter Reservoir in the label field next to the Help
button. Click OK.
☞ The Holding Tank should be set to integrate, rather than sum, its inputs. This will output the value at time 1 that has been calculated for the period from time 0 to 1. These continuous simulation concepts are dis- cussed more thoroughly in “Integration vs. summa- tion in the Holding Tank block” on page 709.
Displaying the results
Holding Tank dialog
Math dialog settings
The Plotter I/O block monitors the total amount of water in the reservoir. (Later in this chapter you will learn different techniques for connecting the Lookup Table and Random Number blocks to the Plotter, to also monitor the amounts flowing in from the rainfall and the stream.)
Double-click the Plotter to open its plotter window.
Notice that the first column in the table is titled Contents. The Plotter automatically named it
when you connected from the contents output of the Holding Tank block.
To further personalize the plotter window:
Click the text label Value in the upper left corner of the Plotter’s graph to select its text box. Type Inches in the text box and click the Tab, Return or Enter key.
Using that same process, change other Plotter labels in the graph pane as follows:
Change Plotter I/O (located at the top of the graph) to Reservoir Model.

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