PLANE-SYMMETRICAL COSMOLOGY WITH RELATIVISTIC HYDRODYNAMICS - ART. NO. 064010

A numerical code, developed for cosmology and to investigate fully non linear behavior in the plane-symmetric Einstein equations, is describe d in detail. The field equations are solved self-consistently with the general relativistic hydrodynamical conservation equations, using art ificial viscosity methods for shock capturing and an ideal fluid stres s-energy tensor with a cosmological constant. Several tests of the cod e are presented, including anisotropically expanding vacuum and isotro pically expanding de Sitter, dust-filled and radiation-filled cosmolog ies, gravitational waves in Bat and anisotropically expanding backgrou nd models, sub- and super-horizon scale density perturbations in an ex panding FLRW background, and both Newtonian and relativistic shock tub e evolutions. Also discussed is a gauge drift instability that can app ear in near-geodesic evolutions of density perturbations when the dyna mical time scale of collapse becomes smaller than the cosmological exp ansion rate. [S0556-2821(98)00918-7].