2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/223898The principle part of Einstein equations in the harmonic gauge consists of a constrained system of 10 curved space wave equations for the components of the space-time metric. A new formulation of constraint-preserving boundary conditions of the Sommerfeld type for such systems has recently been proposed. We implement these boundary conditions in a nonlinear 3D evolution code and test their accuracy.16 pages, 17 figures, submitted to Phys. Rev. DGeneral Relativity and Quantum Cosmologytext