Add a Control Variable Field node () by right-clicking a Component node and choose it from the Control Variables submenu. It is also available on the Definitions ribbon toolbar, form the Optimization menu. Specify the Control Variable Field to add a control variable specific to the geometric entity level (domain, edge, boundary, or point) in question. The field can be accessed via its Name throughout the model.

This section contains settings for the element used to discretize the control variable. Select a Shape function type: Lagrange (the default) or Discontinuous Lagrange. Also select an Element order: Linear, Quadratic (the default), Cubic, Quartic, or Quintic. For Discontinuous Lagrange, one can also pick Constant shape functions. The value type (complex or real) for all the variables defined by this Global Equations node is selected in the Value type when using splitting of complex variables selection. The default value type is Complex.

Here you specify a value of expression for the initial values of the control variable in the Initial value field.

By default, the Use bounds check box is selected so that you can add bounds for the control variable in the Lower bound and Upper bound fields. Note that the bounds are only respected at gauss points, so local violation may occur if the Element order is not either Linear or Constant.

If desired, you can scale the control variable using a scalar value that you enter in the Scale field (default: 1; that is, no scaling). A large scale will generally cause the optimization solvers to take longer steps (MMA without move limits is the exception).