This program models two-dimensional cellular automata.
A cellular automaton is a computational machine that
performs actions based on certain rules.  It can be
thought of as a board which is divided into cells
(such as square cells of a checkerboard).  Each cell can be
either on or off.  This is called the "state" of the cell. 
According to specified rules, each cell will be on (alive)
or off (dead) at the next time step.  In this case of
two-dimensional cellular automata, each cell checks the
state of itself and its eight surrounding neighbors. and then
sets itself to either on or off, depending upon the rule. 
The rule is as follows:  If there are less than two "on"
neighbors, then the cell turns off.  If there are more than
three "on" neighbors, the cell turns off.  If there are 2 "on"
neighbors, the cell remains in the state it is in.  If there
are exactly three "on" neighbors, the cell turns on
This is done in parallel and continues forever.  Cellular
automata can be created on any board size and dimension.
As explained above, Life is a cellular automaton that
simulates the growth, life and death of "organisms".  Their
growth, life or death depends upon the amount of their
neighbors.  There are certain recurring shapes in this
simulation, one of which is the glider.  The glider is
composed of 5 cells which form a small arrow-headed shape.
This glider will "float" across the screen, retaining its
shape.  The glider gun is a large conglomeration of cells
that repeatedly spits out gliders.  A blinker is a block of
3 cells (either up and down or left and right) that rotates 
between horizontal and vertical orientations.

	The DENSITY slider determines the initial density of cells
that are on.  SETUP places these cells.  GO runs the rule
forever.  STEP-ONE runs the rule once.

	ADD-CELLS allows the user to place an "on" cell wherever
the mouse is clicked.  ADD-BLINKER adds a "blinker" wherever
the mouse is clicked, and ADD-GLIDER adds a "glider" heading

	The background color and foreground color can be set via
the sliders.  Just adjust the sliders and click SETCOLORS. 
It may take some experimentation to find the colors that you want.



  Find a "glider gun".

  Find some objects that are alive, but motionless.

  Is there a "critical density" - one at which all change and motion
  stops/eternal motion begins?	


  Are there any recurring shapes other than gliders and blinkers?

  Build some objects that don't die (using "add-cells")

  How much life can the board hold and still remain
  motionless and unchanging? (use "add-cells")


Give some different rules to life and see what happens.

Build a model with nsum4, which uses the cells to the north,
south, east, and west.


nsum count takes the sum of the count variables in the
patches to the north, south, east, west, northeast,
northwest, southeast, and southwest.

nsum4 count takes the sum of the count variables in the
patches to the north, south, east, and west.