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The Function manager (shown in Figure 1) allows you to centrally manage all functions that have been defined in Source. It is used in places where you might otherwise employ a time series or a single value. 

The Function manager can be accessed in one of two ways:

• Choosing View » Function Manager; or
• Clicking on the Function Manager icon in the Scenario toolbar.

Items in the Function manager are sorted into groups, and then by name, and they are ordered as follows:

• In-built functions, which includes End, Now, Start and $ActiveInputSet;
• Variables - there are four types of variables available in Source. Refer to Types of variables for more information;  and
• Custom functions

The $ActiveInputSet function can be referenced as a model variable in another function. It is used to specify the use of a particular input set (if one has been defined). For the function shown in the example below, different values are assigned to the function depending on the value of the variable.

if($ActiveInputSet = "Wet", 15, if($ActiveInputSet = "Dry", 0, 7))

In this case, for all instances of Wet, the function will return a value of 15; for instances of Dry, a value of 7 will be output. All other instances will result in a value of 7.

The Function Manager only shows direct uses of a function. For example, if an inflow node has been assigned a function, $ExampleFunction, this is indicated in the Function Manager. If $ExampleFunction is comprised of two separate functions, $ExFn1 and $ExFn2, these two functions will not be part of the Inflow node.

 You can also search for a variable or function using the area under the Function manager toolbar. Start entering the search item, and the results will be filtered as you type the text.

Function Editor

The Function Editor (shown in Figure 2) allows you to add, modify and delete individual functions and variables. It can be accessed in one of two ways:

• Choosing Edit » Functions…; or
• Choose the variable you want to change in the Function manager (Figure 1). Right click on it, then choose Edit from the contextual menu.

Figure 2. Function Editor

Adding a variable or function

To add a variable or function, click on the Add Variable button on the Functions toolbar (as shown in Figure 1) and choose the appropriate drop-down item;

You can define and configure it using the Configuration pane on the right. The view of this pane will depend on the type of variable or function that has been specified. 

Deleting and renaming a variable or function

To delete a variable or function, choose the appropriate item in the function list, right click, and choose Delete from the contextual menu.

To rename it, choose Rename from the contextual menu and type the name you wish to assign. 

The Results Units drop down menu allows you to choose which units to display the output in.

By default, if a function or variable is not referenced at any node, it is not recorded during a scenario run. The Force Evaluation scroll toggle (Figure 2) ensures that a function is evaluated and recorded during a scenario run. In some cases (eg. if a function is not used in a model), the function will not be evaluated if the scroll if toggled to OFF.

You can also enabling recording of a function using the Project Explorer (choose Miscellaneous).

About variables and functions

Played vs non-played variables

The Function manager distinguishes between two classes of variables:

• Played - These are provided via time series or other inputs such as the Piecewise Linear or Patternsvariables of the Function manager. Conceptually, any played variable can be viewed as a list with the next value taken from the list each time the time-step advances. Played variables are updated at the start of the time-step and maintain the same value throughout the time-step.
• Non-played - Also known as model variables, in which variables are produced by the operation of the models which execute during a run. Within a time-step, the moment when any given model variable is updated depends on the model.

General rules for functions

The following rules apply to functions:

• White-space, including new-line markers, is ignored;
• Function names, operator names, variable names and label names are not case sensitive;
• All variable names must begin with the "$" character;
• All functions are global;
• All variables used in functions must be defined;
• Circular references are prohibited; and
• A blank function returns zero.

	Folder1
		$Function1
		$Function2
	Folder2
		$Function3
	$Function4

For example, you can calculate your place in the water year using the calendar date functions.  

The following features in the Function Manager make it easier to write expressions:

• When you start writing an expression, Source lists all the available arguments, including the in-built variables (such as $now.day and $now.dayofyear). Alternatively, you can press Ctrl + Space on your keyboard to list these options; 
• You can drag and drop variable names into a function;

Testing Functions

Once you have defined an expression or function, you can test its operation using the Parse button. You can enter values for the various terms in your expression and confirm that the result of evaluating your expression with those values is correct. The Parse button is, by default, hidden in the Function editor, and is used as follows:

• Highlight the function you wish to test. This will appear in the Configuration pane of the Function editor;
• Click on the area below the Configuration pane (as shown in Figure 3);
• The expanded section (shown in Figure 4) provides a table of all the variables used in the expression. Enter a value for the variable you wish to test (double-click on the cell, then enter a number);
• Click Parse; and
• The test result will be displayed in the cell under the Parse button.

To close this area, click on the same position.

Figure 4. Function Editor (Parse-window)

If the function cannot be parsed, you will get an error icon next to the function in the Function manager. Additionally, an error in the Log Reporter will indicate the same.

Types of variables

Modelled variables

A modelled variable provides a connection between your function and model (non-played) variables. You define a name (or meta-name) by which you will refer to a model variable in your function and configure other parameters governing its use. Once a variable has been defined, it can be used in a function. To configure a new modelled variable using the Function Editor:

• Add a modelled variable, as described in Adding a variable or function;
• A new variable will appear in the position that was selected. Note that at this point, the variable has not been allocated a recorder, so a warning icon will appear;
• The Configuration pane will show a list of all the recorder variables available (this will depend on the model);
• Using the disclosure triangles, choose the appropriate recorder that you wish to be associated with the variable;
• Depending on the recorder you choose, you can also specify the following:
  • Result Units - units of the results;
  • The variable's Initial Value - this defines the value that the variable takes on between the start of the first time-step and the point during that time-step when the corresponding model variable acquires a defined value;
  • Date Range - the date range that the Function manager uses as a filter when obtaining data during each time-step. For example, you can choose to use the value from the current time-step (assuming it has been updated by the time the function is evaluated) or the previous time-step. You can also use values like the average of the last 100 time-steps. See Date ranges for more information; and 
  • Time of Evaluation - specifies when the variable will be evaluated.