This directory contains C++ code for the horizon finder's basic
multi-patch infrastructure.  This code doesn't know about relativity.

The main classes defined in this directory are as follows:
patch_system
	is the top-level class representing a multipatch system.
	It stores the actual grid function data, defines the actual
	finite differencing operations (both 2nd and 4th order are
	provided, presently selected by #ifdef at compile time),
	and keeps pointers to all the other objects making up the
	patch system.
x_patch, y_patch, z_patch
	represent individual patches near the +/- x, +/- y, and +/- z
	axes respectively.
patch
	is an virtual base class representing a grid patch.
patch_edge
	represents the geometry of a single edge of a patch, ie it
	represents the conversions between (perpendicular,parallel)
	and (rho,sigma) coordinates.
ghost_zone
	is a virtual base class representing the ghost zone
	along a single edge of a patch.
interpatch_ghost_zone
	represents a ghost zone where we get data by interpolating
	it from a neighboring patch.
symmetry_ghost_zone
	represents a ghost zone where we get data by a discrete
	symmetry (eg a reflection or periodic boundary condition).
patch_interp
	is our interface to the interpatch interpolation.

Class  patch  is in term implemented using the following helper classes:
grid
	This class is derived from class  grid_arrays , and adds
	the floating-point grid-coordinate metadata.
grid_arrays
	This class stores the basic integer-array-subscripts metadata
	for a 2-D grid.

The implementation also uses the low-level generic helper template
classes defined in  ../libutil/ .

All the code makes heavy use of the type  fp , defined in  fp.hh .
This is the floating-point type, i.e. CCTK_REAL.


There are also a number of test drivers in  test_*.cc .