	 Simple Systems Exhibiting Self-Directed Replication:
	  Transition Functions, Software, and Documentation

We have recently developed and studied cellular automata models of
self-replicating systems that are substantially simpler than previous
models [Science, 259, 1993, pp. 1282-1288].  The directories here
provide the online version of the various transition functions and
software we used in this study, as well as documentation.  The
cellular automata software included here is actually quite general
and could serve as a fairly application-independent simulator.

Here is a brief description of the contents of each directory:

/Documentation -- 
	This contains technical report CS-TR2965 which includes a
listing of the transition functions and some detailed descriptions
about the software system we developed and used for the discovery of
those transition functions. It is provided both in TeX .dvi format
(tr.dvi) in PostScript(tm) format (tr.ps). Two updated manual pages
for program xca and oca are added to reveal their new functions
(xca.man & oca.man).

You should print the files here and read them if you want to know more
about the system. For a quick start you can go directly to the
/Models directory below. Look at the README file there for more
directions. 

/Models ---
	Self-replicating loops described in the Science paper and their 
transition functions are archived here. For each loop there are five related
files. For example,

	UL06W8V.init 	--- the initial configuration
	UL06W8V.rules 	--- the complete transition functions
	UL06W8V.rules.cp--- the reduced version of the transition
				functions
	UL06W8V.rep 	--- the transition functon which leads to
				replication only
	UL06W8V.rep.cp 	--- the reduced version of above

	A report file is also included in this directory which
contains a summary of the size of each file, counted as number of
rules. Note that two models UL05S6V and UL06S6V were not been
described in the technical report nor the report file.

Another README file is included in this directory which tells you how
to quickly start running these loops using one of the programs, xca,
mentioned below. You can start from here to gain an immediate feeling
about how things work. 

/Systems ---
	All software is stored here. Directions on how to install
these software are included in each directory, either in a README file
or in the C source code file itself.

	/Systems/oca	--- the X11 Window based cellular automata
				simulator which reads the compressed
				version of rule sets
	/Systems/xca	--- a standard X11 Window based celluar
				automata simulator
	/Systems/ca	--- a set of programs which includes a 
				cellular automata simulator and other
				utilities. They are running under the
				Unix command shell and do not require
				the X11 Window system.
	/Systems/ck	--- an implementation of the rule compression
				algorithm
	/Systems/misc	--- some handy small utility programs

A SUN Sparcstation executable is also provided for xca and oca.
Compilation for other architecture should be straightforward as most
programs just use the standard Unix I/O.  Two exceptions are the xca
and oca X11 Window based cellular automata simulators. They are
written based on the Motif(tm) Widget library, so you must have Motif
on your system to recompile them. You also need to modify the
Makefiles contained in both directories to correctly direct the
compiler and linkage editor to the location of the include files and
library for Motif. Look at those Makefiles for details.

The Motif version we have is still 1.0, which has, among other bugs, a
bug with its directory file finding widget. This means that when you try
to load files into the simulator, you will discover that the file
filter does not work. If you have a newer version of Motif, this
problem can be fixed automatically by recompiling those programs.

Although care has been taken while preparing this package, we know
bugs are there somewhere. Since we are not a full fledged commercial
software developing group, constant maintenance and support for this
software package is impossible. Suggestions or bug reports are welcome.
If time permits we will try to fix any bug found and provide an improved
version in the future.

Please send your correspondence to hhchou@eng.umd.edu.

Hui-Hsien Chou
Dept. of Computer Science
A.V. Williams Bldg.
University of Maryland at College Park
College Park, MD 20742 USA



