PK_ERROR_code_t   PK_GROUP_add_entities
(
--- received arguments ---
PK_GROUP_t        group,            --- group
int               n_entities,       --- number of entities (>=0)
const PK_ENTITY_t entities[]        --- entities
)


This function adds the given set of entities to the given group.


Specific Errors:
    PK_ERROR_not_in_same_part       some entity is not in the same part
                                    as the group
    PK_ERROR_wrong_class_for_group  some entity is of a class not allowed
                                    in this group


The new entities should not be existing members of the group.