Epetra_Export: This class builds an export object for efficient exporting of off-processor elements.
Epetra_Export is used to construct a communication plan that can be called repeatedly by computational classes such the Epetra matrix, vector and multivector classes to efficiently send data to a target processor. This class currently has one constructor, taking two Epetra_Map or Epetra_BlockMap objects. The first map specifies the global IDs that are owned by the calling processor. The second map specifies the global IDs of elements that we want to export to later.