Elementary Cellular Automaton in Bash


This is an implementation that generates cell states with Elementary Cellular 
Automaton [1] (ECA) rule and prints out the cell states.


                                  SCREENSHOTS


- rule-110.png, the rightmost cell's initial state is 1.


                                    OPTIONS


* -r for rule number, default is Rule 110
* -n for number of cells, default is half of terminal width
* -i for initial states, default is all 0 but the middle cell


                                IMPLEMENTATION


It implements the tape as array, in cyclic tag system [2], each element is a 
cell, storing '0' and '1' characters which also used in arithmetic evaluation 
as integers 0 and 1.  It does not use bits for cell states.

The main part of ECA is to generate the next cell states, which is implemented 
as:

    ((
        currP = L << 2
              | C << 1
              | R,
        nextC = (RULE_NO >> curr) & 1
    ))

Where

- currP is the current pattern of currently generated cell C with left cell L 
  and right cell R to C as higher and lower bits, three forms a binary.

- nextC is the next state for C, which is a bit in RULE_NO, indexed by currP.

The last line in the code above is a bit copier, which shifts the wanted bit 
(next state) by currP to the lowest bit address, and use bitwise AND to get the 
bit.


                                   COPYRIGHT


This project is licensed under the MIT License.


[1] https://en.wikipedia.org/wiki/Elementary_cellular_automaton
    http://mathworld.wolfram.com/ElementaryCellularAutomaton.html
[2] https://en.wikipedia.org/wiki/Tag_system#Cyclic_tag_systems