There are two methods to create variables to solve for (dependent variables), usually referred to as the unknowns or degrees of freedom (DOF). You can either use a dependent variable or a variable with a shape definition. The dependent variable can only be declared by an interface using the Dependent Variable Declaration under the physics interface. All dependent variables need a shape function definition to add the DOFs that the solver solves for. For this purpose, use the Dependent Variable Definition under a feature or property. If you are unsure what you need, use the default Lagrange shape function.

The other method to create DOFs is to add a shape definition for a variable declared by a Variable Declaration. In contrast to the dependent variable, this variable does not show up in the Model Wizard or in the Settings window for the physics interface instance in the Model Builder. This means that the user cannot change the name of this variable. Another minor difference is that it is possible to define the scope of the variable, where the default is physics scope (<model name>.<physics name>.<variable name>). The dependent variable always has a component scope.