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1994-07-07
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LIFE
Version 2.0
(C) 1994 G.Stretton. Australia.
This is a quick explanation of what life is about.
The basic unit of life is the cell. A cell may be alive or dead. Live cells
are displayed on the screen, dead cells are not.
The rules, changed with edit rules in the control menu, control the fate of
all the cells.
The default rules, 2333, are those used by Conway, the originator of life.
In the rule editor, these rules are shown as:
Die if less neighbours than ---------------------- 2
Minimum number of neighbours for a birth ----- 3
Maximum number of neighbours for a birth ----- 3
Die if less neighbours than ---------------------- 3
A cells neighbours are those cells, alive or dead, that are immediately
adjacent to the cell horizontally, vertically or diagonally. Thus a cell has
eight neighbours which may be alive or dead.
The rules only consider the live neighbours and say:
For every position on the screen:
If the currently considered cell has less than 2 live neighbours then it
dies from lack of companionship.
If the cell is empty and has a minimum of 3 live neighbours and a maximum
of 3 live neighbours, using the default rules exactly 3 live neighbours,
then it is made live, a birth occurs in that cell.
If the cell has more than 3 live neighbours then the cell dies from
overcrowding.
That's it. These simple rules lead to an amazing complexity of behaviour.
This is a bit hard to show here but I will give it a shot.
A * will be used to denote a live cell. Dead cells are not shown.
Consider the pattern of 3 adjacent live cells:
* * *
The pattern of neighbour counts for the surrounding empty cells is:
1 2 3 2 1
1 * * * 1
1 2 3 2 1
By following the rules we find that on the next generation, the pattern has
changed to:
*
*
*
The top and bottom cells were born because they had 3 neighbours.
The left and right cells died because they had less than 2 neighbours and
the centre cell stayed alive because it has 2 neighbours.
If you iterate the rules over this pattern again, it reverts to its starting
position. This is a simple oscillator.
Generation:
1 2 3 4 etc. ......
* *
* * * * * * * *
* *
Another example.
Consider the pattern:
* *
* *
The neighbour count for the cells surrounding this pattern of 4 cells is:
1 2 2 1
2 * * 2 Note that each live cell has 3 live neighbours.
2 * * 2
1 2 2 1
As none of the surrounding empty cells has the requisite number of live
neighbours for a birth, and none of the live cells has more than the
maximum or less than the minimum number of live neighbours to stay alive,
this pattern is stable. It doesn't change from one generation to the next.
That's it really. You may find it helpful to work through a few simple
examples like these using the single step function from the edit menu.
First draw your pattern on the screen using edit section in the edit menu.
Then press the <+> once to calculate the appearance of the next generation.
Press <+> again to display the next generation etc.
See if you can predict the outcome without resorting to the computer.
Then forget all about doing it in your head, as you'll go insane with more
than just a very few live cells on the screen.
I hope this gives you some idea of what the program is about.
If you need more information, then I suggest you look up something
on cellular automata or artificial life at the library.
All the best.
Graeme Stretton.