This class computes map from slave entity to master entity
For entities of dimension dim, compute map from a slave entity on this process (local index) to its master entity (owning process, local index on owner). If a master entity is shared by processes, only one of the owning processes is returned.
This function returns a MeshFunction which marks mesh entities of dimension dim according to:2: slave entities 1: master entities 0: all other entities
It is useful for visualising and debugging the Expression::map function that is used to apply periodic boundary conditions.
The membership flag