The Weak Form PDE (w) interface, found under the Mathematics>PDE Interfaces branch () when adding an interface, is identical to The Coefficient Form PDE Interfaces and The General Form PDE Interfaces except for the default node on the top geometric entity level being a Weak Form PDE node.

In all interfaces, weak expressions can be added, which COMSOL Multiphysics adds to the overall equation. Adding one of these interfaces creates a PDE node () for PDE modeling using a weak formulation. You can also add the same type of Weak Form PDE node on the domain level to any other PDE interface.

When this interface is added, these default nodes are also added to the Model Builder: Weak Form PDE, Zero Flux (for a Weak Form PDE on the domain level only), and Initial Values. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions. On the domain level, edge level, and boundary levels, the same boundary conditions can be used as for the Coefficient Form PDE and General Form PDE. You can also right-click Weak Form PDE to select features from the context menu.

The Label is the default physics interface name.

The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.

The default Name (for the first Weak Form PDE interface in the model) is w (in domains), wb (on boundaries), we (on edges), or wp (at points).