COMSOL Multiphysics includes different PDE interfaces for equation-based modeling, distinguished by the equation formulation used for entering the equations: Coefficient Form, General Form, and Weak Form. The interfaces are identical except for the default node added to the top geometric entity level where the interface is active. You can still use a General Form to specify equations in a Coefficient Form PDE interface, or add Weak Form contributions to a General Form PDE interface.