Applets are small pieces of Java^TM program written to work inside a browser page. All the examples on these pages use two applets that I wrote to illustrate Cellular Automata:

LifeApplet

An applet to illustrate the Game of Life

CAApplet

An applet to illustrate 1-Dimension 2-State CA

This is based loosely on a program I wrote about 20 years ago for the original IBM PC (that program was itself based on an earlier one on the IBM 370 mainframe, and I would like to acknowledge the colleague from that time who suggested the outline of the algorithm, except that I've forgotten his name — sorry).

The PC program used CGA graphics to write to the screen, and that's the way I've thought of Life ever since — green on black. So those are the colors I chose as defaults for the applet.

If you want to include the applet in your own pages, try the following HTML:

<applet code="net.pwall.ca.LifeApplet.class"
        codebase="http://pwall.net/applet"
        width="360" height="360">
    <param name="name" value="value">
</applet>

The parameters are:

Name	Description	Default
cellsize	Number of pixels per cell	3
cycle	Milliseconds per cycle	100
start	Starting pattern	r-pentamino
empty	Color for empty cells (in #xxxxxx form)	black
filled	Color for filled cells (see above)	green
text	Color for text (see above)	black
bg	Color for background (see above)	white

The applet will adapt to whatever width and height parameters are supplied on the applet element, and will take sensible defaults for all values. The alternatives for start are:

block

a 2x2 block to illustrate a stable configuration

blinker

a three-in-a-row blinker

grid

a grid of blocks filling the whole area, with one missing in the middle to make things interesting

This applet was written to illustrate my commentary on Stephen Wolfram's book A New Kind Of Science.

If you want to include this applet in your own pages, use the following HTML:

<applet code="net.pwall.ca.CAApplet.class"
        codebase="http://pwall.net/applet"
        width="361" height="361">
    <param name="name" value="value">
</applet>

The parameters are:

Name	Description	Default
ruleset	The rule set in Wolfram's numbering scheme	110
cycle	Milliseconds per cycle	20
max	Maximum number of cycles	varies
array	Size of array	3201
empty	Color for empty cells (in #xxxxxx form)	white
filled	Color for filled cells (see above)	black

The applet will adapt to whatever width and height parameters are supplied on the applet element, and will take sensible defaults for all values. Odd widths (and array sizes) are preferred since that means symmetrical patterns will appear symmetrical on the page.

The starting position is always a single black cell, usually in the center of the array. For rule set 110, which always expands to the left but not to the right, the starting cell is positioned one place in from the extreme right-hand edge.

The default number of cycles will vary according to the width and the rule set, and will always be set to stop just before edge effects (see below) start to kick in.

You are welcome to use either of these applets, provided you prominently acknowledge the source of the applets, acknowledge my copyright in the applets and include a reference to this page. Please notify me (see email link at the top of this page) if the applets are used in any publicly-accessible pages.

A word here about edge effects. Both Life and the 1-Dimension Cellular Automata discussed here presuppose an infinite "universe" — in the case of Life, an infinite plane, and for a 1-D CA, an infinite line. The Java applets operate on finite arrays, which means that the results are not strictly correct.

In the case of Life, the applet operates as if the visible area is surrounded by dead cells, and that these can never give birth. The effect on a glider which hits the edge is to turn it into a block. (The original pattern in the main example on the previous page was positioned so that no other edge effects would distort the result).

For the 1-D CA, this approach wasn't very successful. The edge effects came into play much earlier than for Life, and made it difficult to get useful results. So for these, I chose to make the array many times larger than is visible on the screen, and by default, the applet stops cycling the CA before edge effects can take place.

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