WHAT IS IT? ----------- 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. HOW TO USE IT ------------- 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 southeast. 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. RUNNING the MODEL ----------------- THINGS TO NOTICE ---------------- 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? THINGS TO TRY ------------- 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") EXTENDING THE MODEL ------------------- 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. STARLOGO FEATURES _________________ 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.