Working with the Function manager

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. Refer to the User interface reference for more information about the Function Manager toolbar.

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. Groups are ordered as follows:

• Folders associated with In-built variables, such as End (refer to In-built functions and variables, default date ranges);
• Functions;
• Variables - there are five types of variables available in Source. Refer to Types of functions and variables for more information; and
• Custom functions.

Usages

When a function is used in a model (in an inflow node for example), then that usage is shown in the tree under the function. If a function is used in multiple places, then all usages are shown under the function in the Function Manager tree. To link a node to a function, either:

• Use the node's feature editor; or
• Right click the function and choose Add Usage. Then, use the Adding function usages manually.

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 Search field under the Function manager toolbar. Start entering the search item, and 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
• In the Function manager, choose the variable you want to change. Right click on it, then choose Edit from the contextual menu.

Figure 2. Function Editor

Features of the Function Editor include:

• The pane on the left side is the same as that in the Function Manager. Hence, the contextual menus available are the same as those available in the Function Manager;
• The Results Units drop down menu allows you to choose which units the variable or function will evaluate to. The result units of a function have to commensurate to the required units of the model input it is used for. If the result units of the function are not the same as the required units of the model input, a conversion is done of the function result before it passes the value to the model;
• By default, if a function is not referenced at any model input, or any other functions, it is not evaluated during a scenario run. The Force Evaluation scroll toggle ensures that a function is evaluated during a scenario run. This is generally used when you wish to record a function that is not used, or if a modelled variable points to a function that is not evaluated. Note that if you toggle this on for all functions, system performance is reduced;
• For a function, the Initial Value is used when a function references itself and is the first evaluation of the function. For the storage node, initial values are used until the modeled variable or function is used/executed for the first time. For example, the initial value can be used until the function evaluated. This means that even on the first time-step, it may not be used depending on the evaluation times. For arrays, the initial values is used until the array is full - for example, if you have a date range of a week; and
• You can also enable recording of a function using the Project Explorer (choose Miscellaneous).

Working with functions

Note the following:

• Source evaluates the function equation for each time-step and returns a singlevalue for each time-step. The will be the last evaluated value for the function;
• 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 variables used in functions must be defined;
• Functions can reference themselves. The initial value is used in this case for the first evaluation of the function;
• There are several in-built functions and operators that allow you to define otherwise complex functions in simple expressions. A complete list is provided here;
• Circular references are prohibited between multiple functions; and
• A blank function returns zero.

Other useful features

The following features in Source are available when writing functions: 

Scoping

Functions and variables can have non-unique names, so long as they are in different scopes. For example, consider the setup shown in Figures 4 and 5:

Figure 4. Function Editor, Scoping example 1

Figure 5. Function Editor, Scoping example 2

• $Function1’s expression can reference $Function2 directly as they are both part of Folder1. So, if($Function2, 0, 1) is a valid function - Figure 4;
• If $Function3 references $Function2, you must use the full path to reference it - if($Folder1.Function2, 0, 1) - Figure 5; and
• Any function can reference $Function4 directly because it is in the global scope (ie. it is not part of a folder).

Adding a variable or function

Follow these steps to add a variable or function:

• Click on the Add Variable button in the Functions toolbar (as shown in Figure 1) and choose the appropriate drop-down item. This can be done in the Function manager (Figure 1) or Function Editor (Figure 2);
• 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; and
• The view of the pane on the right will depend on the type of variable or function that has been specified.

The function/variable can now be defined.

Adding a note to a function

You can include a text-based message, or note, to be associated with a function. Refer to About notes for more information.

To associate a note with a function (as shown in Figure 6):

• Open the Function Editor;
• Click on the function you want to add a note to;
• In the Function Editor toolbar, click on the Add/Edit Note icon; and
• Add the text message in the window that appears.

Figure 6. Function Editor, Adding a note

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. 

Operator precedence

Unless you use parentheses to modify the order of evaluation, operations are performed according to the precedence rules shown in Table 1. Where two operators have the same level of precedence, the operations are performed left-to-right.

Table 1. Function Editor (Evaluation order)

Referencing

A function can reference other functions within the same scenario. It can also reference itself. 

For example: $Function1 = $Function1 + $Function2
In this case, $Function1 will use its previous evaluation value to calculate its new one.

Notice that the list shown in Figure 3 contains $Function1 as an option. 

Testing Functions

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

• Select the function you wish to test. This will appear in the right side pane of the Function editor;
• Click on the arrow next to Parser (as shown in Figure 7);
• If the variables/functions used in the function are not in the list, click Parse
• The expanded section (shown in Figure 8) provides a table of all the variables used in the function. 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 arrow.

Figure 8. 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 be available at run time to indicate the same.

Time of Evaluation

Functions are evaluated at the start of each time-step. Simulation phases shows details of all phases involved in a simulation time-step:

• start of the ordering phase;
• end of the ordering phase;
• start of the flow distribution phase; or
• end of the flow distribution phase.

Date ranges