Registering Coordinates and Coordinate Properties

Coordinate systems and their properties can be registered at any time with the Flesh. The registration utilities for thorns providing coordinates are:

CCTK_CoordRegisterSystem

Assigns a coordinate system with a chosen name and dimension. For example, a 3-dimensional Cartesian coordinate system could be registered with the name cart3d using the call from C

int ierr;
int dim=3;
ierr = CCTK_CoordRegisterSystem(dim,"cart3d");

CCTK_CoordRegisterData

Defines a coordinate in a given coordinate system, with a given direction and name, and optionally associates it to a grid variable. The directions of the coordinates range from 1 to the dimension of the coordinate system. For example, to register the grid variable grid::y3d to have the coordinate name y in the cart3d system

int ierr;
int dir=2;
ierr = CCTK_CoordRegisterData(dir,"grid::y3d","y","cart3d");

CCTK_CoordRegisterRange

Assigns the global computational maximum and minimum for a coordinate on a grid hierarchy, that is in a cctkGH. At this time the maximum and minimum values have to be of type CCTK_REAL. For example, if the y coordinate for the cart3d system ranges between zero and one

CCTK_REAL lower=0;
CCTK_REAL upper=1;
int ierr;
ierr = CCTK_CoordRegisterRange(cctkGH, lower, upper, -1, "y", "cart3d");

Note that the API allows either the coordinate name or the direction to be used, so that the following is also valid

CCTK_REAL lower=0;
CCTK_REAL upper=1;
int ierr;
ierr = CCTK_CoordRegisterRange(cctkGH, lower, upper, 2, NULL, "cart3d");

CCTK_CoordRegisterPhysIndex

Implementing such things as symmetry properties for a grid leads to the need to know the details of the physical section of a grid. Such information is typically needed by IO thorns. The following call illustrates how to register the indices 3 and 25 as supplying the physical range of the y coordinate in the cart3d system

int loweri=3;
int upperi=25;
int ierr;
ierr = CCTK_CoordRegisterPhysIndex(cctkGH, loweri, upperi, -1, "y", "cart3d");