## Information and Tools

A BC is an object that represents a PDE boundary condition. It is applied to select boundaries of the simulation domain using the boundary parameter in the relevant sub-block of the ADBCs block of a MOOSE input file. There are two different flavors of BCs: IntegratedBCs and NodalBCs. IntegratedBCs are integrated over the domain boundary and are imposed weakly. NodalBCs are applied strongly at individual nodes and are not integrated. An AD prefix, as in ADNodalBC, indicates that the Jacobians for subclasses deriving from the parent type are computed using automatic differentiation. In an ADBC subclass the computeQpResidual() function must be overridden.
To create a custom ADNodalBC, you can follow the pattern of the ADFunctionDirichletBC object implemented and included in the MOOSE framework. For demonstration of an ADIntegratedBC, you can refer to the ADRobinBC test object.