Purpose

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.