Einstein Toolkit standards

Einstein Toolkit Standards

ADMBase

Thorn ADMBase provides core infrastructure for thorns implementing general relativity on a 3D grid in the 3+1 formalism. It provides the basic variables (3-metric, extrinsic curvature, lapse and shift vector) for the 3+1 formalism, in addition to a set of parameters to regulate the methods used for their evolution. These variables are used to communicate between thorns providing initial data, evolution methods and analysis routines for the 3+1 formalism. In addition, the variables can be used as a mechanism to interact with alternative formalisms, as long as routines can be written to transform alternative variables into these 3+1 variables. (Taken from the ADMBase documentation)

The Einstein Toolkit uses this thorn for ensuring that different analysis and initial data thorns are able to communicate with evolution thorns, independently of the variables which are used for performing the Einstein evolution. Generally speaking, an initial data thorn will set the ADMBase variables (gxx, gxy, ..., kxx, kxy, ..., alp, betax, ...) to the required initial data. An evolution thorn will import the ADMBase variables into its evolution variables (e.g. for BSSN this might be phi, gammaTilde11, ...) and perform the evolution using these variables. On every time step, it will update the ADMBase variables from the evolved variables so that the ADMBase variables always contains the current solution. Analysis thorns such as those for horizon-finding or wave extraction then use the ADMBase variables, meaning that they can be used in simulations with any evolution thorn which uses the ADMBase mechanism.

See the ADMBase documentation for more information.