Testing The Cactus Code On Exact Solutions Of The Einstein Field Equations
The article presents a series of numerical simulations of exact solutions of the Einstein equations performed using the Cactus code, a complete three-dimensional machinery for numerical relativity. We describe an application ("thorn") for the Cactus code that can be used for evolving a variety of exact solutions, with and without matter, including solutions used in modern cosmology for modeling the early stages of the universe. Our main purpose has been to test the Cactus code on these well-known examples, focusing mainly on the stability and convergence of the code.

title: Algebraic Programming in the Hamiltonian Treatment of the Einstein–Maxwell Equations
abstract: We present new procedures in REDUCE language using the EXCALC package (adapted for IBM-PC machines) for algebraic programming in the hamiltonian formulation of Einstein–Maxwell equations. The dynamic and the constraint equations containing specific terms of the interaction of gravity with source-free electromagnetic field are translated into computer procedures. The results obtained by processing some examples of space-time models are presented.

title: Gravity, torsion, Dirac field and computer algebra using MAPLE and REDUCE
abstract: The article presents computer algebra procedures and routines applied to the study of the Dirac field on curved spacetimes. The main part of the procedures is devoted to the construction of Pauli and Dirac matrices algebra on an anholonomic orthonormal reference frame. Then these procedures are used to compute the Dirac equation on curved spacetimes in a sequence of special dedicated routines. A comparative review of such procedures obtained for two computer algebra platforms (REDUCE + EXCALC and MAPLE + GRTensorII) is carried out. Applications for the calculus of Dirac equation on specific examples of spacetimes with or without torsion are pointed out.

title: Classical Gaussian bag in (1+1) general relativity
abstract: Relativistic geometric models generated by Gaussian conformally flat (1+1) metrics are considered. These metrics are depending on a fixed parameter and another variable parameter that play the role of coupling constant. It is shown that these models are of open bags where the relativistic massive particles remain confined for energies less than the rest one. By using numeric methods it is pointed out that inside of the bag the motion is close to an harmonic one. The dispersion function is also calculated for different values of the free parameter.

title: The use of the algebraic programming in teaching general relativity
abstract: The article presents some aspects on the use of computer in teaching general relativity for undergraduate students with some experience in computer manipulation. The article presents some simple algebraic programming (in REDUCE+EXCALC package) procedures for obtaining and the study of some exact solutions of the Einstein equations in order to convince a dedicated student in general relativity about the utility of a computer algebra system.

title: Maple+GrTensorII libraries for cosmology
abstract: The article mainly presents some results in using MAPLE platform for computer algebra (CA) and GrTensorII package in doing calculations for theoretical and numerical cosmology.

title: Classical oscillators in general relativity
abstract: It is shown that in general relativity some static metrics are able to simulate oscillatory motions. Their form depends on two arbitrary real parameters which determine the specific oscillation modes. The conclusion is that these metrics can be used for new geometric models of closed or even open bags.