README  README  README  README  README  README  README  README  README  README

								  22 June 1993

    This is the fourth release of the hierarchical N-body program.  The
algorithm used to compute gravitational forces has asymptotic complexity of
O(N log N).  This is achieved by building a tree structure to represent the
mass distribution and estimating forces by a partial recursive descent of this
tree.  See "A Hierarchical O(N log N) Force Calculation Algorithm", by Joshua
Barnes and Piet Hut, Nature, 324, 446, and "Error Analysis of a Tree Code", by
Joshua Barnes and Piet Hut, Astrophysical Journal Supplement, 70, 389, for
more information.

    The code has been rewritten in ANSI C for greater portability.  Prototypes
have been provided for all functions.  Several functions associated with tree
construction have been simplified; the resulting code should be easier to
mantain.  Force calculation has been made more accurate by incorporating a new
opening-angle criterion, and faster by adding additional pointers to the tree
structure.  Quadrupole corrections for body-cell interactions are now included
as a run-time option; see "Performance Characteristics of Tree Codes", by Lars
Hernquist, Astrophysical Journal Supplement, 64, 715.

    The source files for the tree code have been bundled together for ease of
distribution.  On a UNIX system, you can split this file simply by invoking
the Bourne shell on it (use the sh command).  On other systems, you may have
to edit this file and split it up by hand; note that file X is delimited by
lines containing the message End of X.  Once you have split this file, you can
compile it by running make on a UNIX system.  On other systems, you are on
your own; take a look at the Makefile for hints.  Running the program with the
default input parameters (type a <CR> to all prompts) will start a short
calculation with a few particles to test things out.

    These sources include a few files which you may find generally useful:
"stdinc.h", a standard include file with common definitions, "vectmath.h", a
set of macros for elementary vector and matrix operations, "real.h", a set of
definitions for floating-point code, "getparam.c", a simple, standardized user
interface, and "util.c", some miscellaneous utilities.  These are part of a
larger collection of software for numerical experiments with gravitating
systems.

    NO WARRANTY is offered on the software supplied here -- use it at your own
risk.  NO RESTRICTIONS are imposed on use and distribution of the code -- you
are free to use this software for any application, modify it in any way, use
pieces in other programs, and give it away to anyone else.  You are encouraged
to extend these rights to others who receive this software from you, following
the philosophy and intentions of the Free Software Foundation.

    You are asked to include a brief acknowledgement in any scientific papers
you write using this code; I would appreciate receiving preprints or reprints
of such papers.  I would also appreciate receiving reports of bugs and/or
problems encountered in porting this code to other machines.

    Have fun and stay in touch.

	Joshua E. Barnes			barnes@zeno.ifa.hawaii.edu

	Institute for Astronomy			(808) 956-8138
	University of Hawaii
	2680 Woodlawn Drive
	Honolulu, Hawaii  96822

README  README  README  README  README  README  README  README  README  README