=== Running a Parametric Sweep with SBR ===
[[File:prop_run24.png|thumb|300px|EM.CUBE's variable dialog]]
[[File:prop_run23.png|thumb|250px|Dialog for defining new variables]]
In EM.CUBE, all the CAD object properties as well as certain source, material and mesh parameters can be assigned as [[variables]]. [[Variables]] are defined to control and vary the values of such parameters either for editing purposes or to run parametric sweep or [[optimization]]. Variable are defined using the '''[[Variables]] Dialog''', which can be accessed in the three ways:
The [[variables]] dialog is initially empty. To add a new variable, click the '''Add''' button to open up the '''Add Variable/Syntax Dialog'''. In this dialog you have to type in a name for the new variable and choose a type. The default type is '''Uniformly Spaced Samples'''. You also need to specify the '''Start''', '''Stop''' and '''Step''' values for the variable. In the figure below, a variable called "Tx_Height" is defined that varies between 2 and 10 with equal steps of 2. This means the sample set {2,4,6,8,10}. When you return to the [[variables]] dialog, the syntax of the new variable is shown as 2:10:2. The last number in this syntax is always the variable step. In this example, this variable is going to be used to control the height of the transmitter in a propagation scene.
[[File:prop_run24.png]] [[File:prop_run23.png]]
EM.CUBE's variable dialog and the dialog for defining a new variable.
Next, you have to attach the variable to the CAD object. In this case, the CAD object is the point object that represents the transmitter's radiator. To attach a variable to a CAD object, open the object's property dialog and type in the name of the variable as the value of a property or parameter. In this case, the variable Tx_Height is going to control the Z-Coordinate of the point object. Once the value of the object parameter is replaced by the name of an already defined variable, it is updated with the current value of that variable. In the case of a variable of "Uniformly Spaced Samples" type, the current value is the start value. This value will be incrementally varied during a parametric sweep simulation process. Note that a variable can take a fixed value or a discrete set of values, too. You can always open the [[variables]] dialog and change the value or syntax of any variable. To make a new or modified value effective, click the '''Apply''' button of the [[variables]] dialog. You can test the values by performing a '''Dry Run''' of the selected variable. This runs an animation of the project workspace as the value of the variable changes and all the related CAD objects are updated accordingly. Note that you can attach the same variable to more than one CAD object property or to the properties of different objects. You can also define multiple values or syntaxes to the same variable. To do so, open the '''Add Variable/Syntax Dialog''', and instead of typing in a new variable name, choose an existing variable name from the '''Name''' dropdown list. This will add a new value or syntax to the existing syntax(es) of the selected variable. When you return to the [[variables]] dialog, [[variables]] with more than one value or syntax will have a dropdown list in the '''Syntax''' column. You can choose any of these values or syntaxed at any time and make the change effective by clicking the '''Apply''' button.
Choosing parametric sweep as the simulation mode in the run dialog. Note that one variable has been defined and EM.CUBE is ready to run the simulation.
[[File:prop_run27_tn.png|800px]]
The coverage map of the scene at the end of a parametric sweep where the sweep variable is the transmitter height.