What is the ICE Applet?
The applet above executes what is called a genetic algorithm (GA). To facilitate understanding, every step in the GA is animated. This particular GA evolves solutions to a simple board game I created just for this purpose. This program also detects and reports if any irreducibly complex (IC) solutions arise during the evolution of its population of solutions to the board game. Click here for more information on the concept of irreducible complexity. Click here for more information on Genetic Algorithms.
The Control Bar
After clicking anywhere on the title screen, the applet will display the following control bar.
The seven controls are, from left to right, the Play/Pause button, the Slow Speed button, the Medium Speed button, the Fast Speed button, the IC button, the Threshold button, and the Exit button.
Play/Pause Button
Clicking the Play/Pause button starts and stops the GA animation, as the name implies. Initially the animation is stopped and this button must be clicked to begin the GA.
Slow Speed, Medium Speed, and Fast Speed
These three buttons control the speed of the animation. Slow and medium speeds are for observing the details of the GA in operation. Fast speed is considerably quicker than both the slow and medium speed. When set to fast speed, entire generations tick by in fractions of a second. Use slow and medium speed to learn how the GA functions and how the board game works; use fast speed to rush ahead many generations.
IC Button
The IC button toggles the GA between two modes. In the first mode ("IC" in black text) the GA will check every individual it produces to see if it is irreducibly complex (IC). An individual will be considered IC if the following three conditions hold:
If an IC individual is discovered, the animation will pause, and the message "THIS INDIVIDUAL IS I.C." will be displayed.
In the second mode ("IC" in gray text) the GA will not bother checking for IC.
Threshold Button
The Threshold button (the circle with the letter "T") toggles the GA between another two modes. In the first mode (letter "T" in black text) the initial value of the game ball will drop by one point whenever an individual evolves with fitness greater than a particular threshold (50). See below for an explanation of the game ball, and how its initial value affects fitness. A lower initial value for the game ball makes the game more difficult, so when it drops all individuals in the population must have their fitness recalculated. Keep the GA in threshold mode to produce an IC individual (doesn't always happen, of course).
Exit Button
Clicking the Exit button (the circle with the letter "X") takes you back to the title screen, and the program resets.
The Board Game
The GA evolves a population of solutions to a board game I made up. Here is a snapshot of the game in play.
The game board consists of 100 boxes in ten rows and ten columns. The game ball (a circle with a number in it) falls downward through the game board until it reaches the bottom and falls off. Along the way it can move down, left, or right, but never up. The number written in the ball indicates its point value. The value of the ball can change as it falls through the board, and its initial value (15 points) can change from generation to generation (see "Threshold Button" above). The ball enters in column four, which is marked at the top of the board by a purple rectangle. The ball will continue moving straight down until it encounters one of the following four types of boxes, indicated with the letters S, A, L, and R:
S ("Split" box)
When a game ball passes through a Split box, it gets split into two balls, each having the same value as the original. If the original ball enters from above, the two balls emerge headed left and right. If the original ball enters from the right, one emerges headed right, the other down. If the original ball enters from the left, one emerges headed left, the other down. The only exceptions are Split boxes at the far left/right of the board (columns 0 and 9) which don't split game balls at all since the extra ball would have nowhere to go.
A ("Add" box)
When a game ball passes through an Add box, its value increases by one point. Also, it continues moving in the same direction it was headed when it entered the box.
L ("Left" box)
When a game ball encounters a Left box, it attempts to make a left turn (from the ball's point of view). When entering from the left, a left turn would point the ball upward, which is not allowed, and in such a case the ball exits the box headed down.
R ("Right" box)
When a game ball encounters a Right box, it attempts to make a right turn (from the ball's point of view). Just as with Left boxes, upward motion is not allowed, and a ball entering from the right will be pointed downward instead.
Representation
The Split, Add, Left and Right boxes on the game board come from the "genetic" material of an individual in the population. The individual (or solution) is shown as three strings of digits and letters below the game board. The first string indicates which columns the Split, Add, Left and Right boxes go in, the second line indicates which rows, and the third indicates which types of boxes. In the snapshot above, for example, the first letters of each line indicate that in column 3, row 5 there should be a Left box (L). The individual is "decoded" from left to right, so that if more than one box is specified for the same location on the board, the one furthest right in the "genetic" material ends up on the final game board.
Keeping Score / Fitness
At the bottom of the game board, in red text, is the number of points collected ("0 pts" in the snapshot image above). Only balls that fall off the board in column five (marked at the bottom by a purple rectangle) get their points added to the total. Once all game balls have fallen off the board, the fitness of the solution is calculated as: total points subtract length of "genetic" material. Subtracting the length of the "genetic" material can be thought of as a kind of selection pressure put on the population to coax individuals to get more points with fewer boxes. A fitness value less than or equal to zero is considered a non-solution, and such individuals are "dead". Since fitness values below zero are just as good as zero, negative fitness values are changed to be zero. Unless the entire population has fitness zero, such "dead" individuals are not available as parents for the next generation.
Generations
A single generation in the GA has three steps:
The current generation number is shown in small text below the game board.
Population
The 20 individuals making up the GA population are shown to either side of the game board. They will move about on screen as they take part in various GA operations such as fitness evaluation, mutation, and crossover.
Downloads
Click here to download a zip archive of all the files needed to run this applet on your home computer.
Click here to download a zip archive of the source code (in Java).