Add a Weak Contribution node () under Definitions > Equation Contributions in a model component to add a weak expression integrated on a selection to the overall system of equations.

The Settings window contains the following sections:

Select the Geometric entity level of the selection over which the weak expression is to be integrated. The default level is the Domain level.

If the component where the weak contribution is added contains attached extra dimensions, optionally select a valid attached dimension from the Extra dimension attachment list and specify a selection in the attached extra dimension. This will also filter the base selection, which will be applicable only where the extra dimension has been attached.

When the Geometric Entity Level is set to Boundary, you can extend the selection to include all boundaries between individual mesh elements inside a domain selection. Note that the selection is specified on the domain level, but the resulting selection is still a boundary selection.

Enter a Weak expression valid on the feature selection.

Choose a suggested Integration order or User defined which will expose the Order expression field. The suggested even orders from 0 to 8 are available in all dimensions. The default is 4 which is appropriate for a second-order equation using quadratic shape functions. An order entered as a user-defined parameter expression must evaluate to an integer, but may be odd. The maximum order depends on the space dimension. It is 30 in 2D and 14 in 3D.

Choose a frame from the Integrate on frame list to set the volume element in the weak form integral. The default is Spatial.