Base class of all partitioned flux-side (Neumann) coupling BCs: sets the patch-normal gradient so that the diffusive flux balances the interpolated flux of the value-side partner plus a flux jump, and relaxes it with an acceleration model.
Base class of all partitioned value-side (Dirichlet) coupling BCs: sets the patch value to the interpolated neighbour value plus a value jump, relaxes it with an acceleration model and supplies its diffusive flux to the flux-side partner.
Partitioned flux-side coupling BC for any scalar field: fixes the normal gradient so that the diffusive flux balances the flux of the value-side partner (zero flux jump), for use with any interface type.
Partitioned value-side coupling BC for any scalar field: fixes the patch value to the interpolated neighbour value times an optional partition coefficient, for use with any interface type.