A general variable acts as substitute for another object and is used when the model creator wants to present users with different options for a certain calculation.
From the Projects window
From the Model window
From the Blocks window
The block editor is shown by right-clicking the block in a window and selecting Edit. In the Blocks window, you can also show the block editor by selecting the block and clicking the button, or by double-clicking the right-most “validation” column of the block.
The block editor has three tabs:
This page lets you edit basic properties such as name, sub-system and base unit. See editing properties for more information.
|Note||Most block properties can be edited directly in the Blocks window.|
Dimension - You can specify the dimension of the block by using the Type drop down list. Depending on the dimension the index drop down lists are activated. See editing values for more information.
The deposition of a contaminant onto soil can be specified in different ways depending on the scenario. In one scenario, the user might have time dependent measurements for deposition. In another the deposition is constant. In a third the deposition is calculated as a function of temperature, the concentration in air etc.
Rather than building three different models, the modeller creates one object for each scenario: a lookup table, a parameter and an expression. He then creates a general variable and calls it “deposition strategy”. Finally the modeller adds the three objects to the general variable and selects one of them. The general variable can now be used in equations, and will delegate to the selected object.
A user can easily change the strategy simply by editing the general variable and select the apropriate object.