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Life-like cellular automaton


A cellular automaton (CA) is Life-like (in the sense of being similar to Conway's Game of Life) if it meets the following criteria:

This class of cellular automata is named for the Game of Life (B3/S23), the most famous cellular automaton, which meets all of these criteria. Many different terms are used to describe this class. It is common to refer to it as the "Life family" or to simply use phrases like "similar to Life".

There are three standard notations for describing these rules, that are similar to each other but incompatible. Wolfram & Packard (1985) use the Wolfram code, a decimal number the binary representation of which has bits that correspond to each possible number of neighbors and state of a cell; the bits of this number are zero or one accordingly as a cell with that neighborhood is dead or alive in the next generation. The other two notations unpack the same sequence of bits into a string of characters that is more easily read by a human.

In the notation used by Mirek's Cellebration, a rule is written as a string x/y where each of x and y is a sequence of distinct digits from 0 to 8, in numerical order. The presence of a digit d in the x string means that a live cell with d live neighbors survives into the next generation of the pattern, and the presence of d in the y string means that a dead cell with d live neighbors becomes alive in the next generation. For instance, in this notation, Conway's Game of Life is denoted 23/3.

In the notation used by the Golly open-source cellular automaton package and in the RLE format for storing cellular automaton patterns, a rule is written in the form By/Sx where x and y are the same as in the MCell notation. Thus, in this notation, Conway's Game of Life is denoted B3/S23. The "B" in this format stands for "birth" and the "S" stands for "survival".

There are 218 = 262,144 possible Life-like rules, only a small fraction of which have been studied in any detail. In the descriptions below, all rules are specified in Golly/RLE format.

Several more rules are listed and described in the MCell rule list and by Eppstein (2010), including some rules with B0 in which the background of the field of cells alternates between live and dead at each step.


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