Analysis of ``Gauge Modes'' in Linearized Relativity
  By writing the complete set of $3 + 1$ (ADM) equations for linearized waves, we are able to demonstrate the properties of the initial data and of the evolution of a wave problem set by Alcubierre and Schutz. We show that the gauge modes and constraint error modes arise in a straightforward way in the analysis, and are of a form which will be controlled in any well specified convergent computational discretization of the differential equations. 
Richard A. Matzner, Mijan Huq, Alonso Botero, Dae Il Choi, Ullar Kask,   Juan Lara, Steven Liebling, David Neilsen, Premana ...