paper available

[mm@santafe.edu]

Though not about connectionist networks, the following TR may be of interest 
to readers of this list:

-----------------------------
The following paper is available by public ftp.

		      Revisiting the Edge of Chaos: 
	    Evolving Cellular Automata to Perform Computations
	
   Melanie Mitchell       Peter T. Hraber         James P. Crutchfield
  Santa Fe Institute    Santa Fe Institute  University of California, Berkeley

              Santa Fe Institute Working Paper 93-03-014

                                Abstract

We present results from an experiment similar to one performed by
Packard (1988), in which a genetic algorithm is used to evolve 
cellular automata (CA) to perform a particular computational task.  Packard
examined the frequency of evolved CA rules as a function of Langton's 
lambda parameter (Langton, 1990), and interpreted the results of his 
experiment as giving evidence for the following two hypotheses:
(1) CA rules able to perform complex computations are most likely
to be found near ``critical'' lambda values, which have been claimed
to correlate with a phase transition between ordered and chaotic behavioral
regimes for CA;  (2) When CA rules are evolved to perform a complex
computation, evolution will tend to select rules with lambda values
close to the critical values.   Our experiment produced very different results,
and we suggest that the interpretation of the original results is not 
correct.  We also review and discuss issues related to lambda, 
dynamical-behavior classes, and computation in CA.  

The main constructive results of our study are identifying the emergence 
and competition of computational strategies and analyzing the central
role of symmetries in an evolutionary system. In particular, we
demonstrate how symmetry breaking can impede the evolution toward
higher computational capability.


To obtain an electronic copy:

	ftp santafe.edu
	login: anonymous
	password: <your email address>
	cd /pub/Users/mm
	binary
	get rev-edge.ps.Z 
	quit

Then at your system:

	uncompress rev-edge.ps.Z
	lpr -P<printer-name> rev-edge.ps


To obtain a hard copy, send a request to mm at santafe.edu.