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CellularAutomaton

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CellularAutomaton[rule, init, t]
generates a list representing the evolution of the cellular automaton with the specified rule from initial condition init for t steps.
CellularAutomaton[rule, init]
gives the result of evolving init for one step.
CellularAutomaton[rule, init, {tspec, xspec, ...}]
gives only those parts of the evolution specified by tspec, xspec, etc.
CellularAutomaton[rule, init, {t, All, ...}]
includes at each step all cells that could be affected over the course of t steps.
  • Possible forms for rule are:
nk=2, r=1, elementary rule with rule number n
{n,k}general nearest-neighbor rule with k colors
{n,k,r}general rule with k colors and range r
{n,k,{r1,r2,...,rd}}d-dimensional rule with (2 r_1+1)×(2 r_2+1)×…×(2 r_d+1) neighborhood
{n,k,{{off1},{off2},...,{offs}}} rule with neighbors at specified offsets
{n,k,rspec,s}order-s rule
{n,{k,1}}k-color nearest-neighbor totalistic rule
{n,{k,1},r}k-color range r totalistic rule
{n,{k,{wt1,wt2,...}},rspec}rule in which neighbor i is assigned weight wti
{lhs1->rhs1,lhs2->rhs2,...}explicit replacements for lists of neighbors
{fun,{},rspec}function fun to apply to each list of neighbors
  • Common forms for 2D cellular automata include:
{n,{k,1},{1,1}}9-neighbor totalistic rule
{n,{k,{{0,1,0},{1,1,1},{0,1,0}}},{1,1}}
5-neighbor totalistic rule
{n,{k,{{0,k,0},{k,1,k},{0,k,0}}},{1,1}}
5-neighbor outer totalistic rule
  • The number of possible cellular automaton rules is as follows:
elementary rules256
1D general rulesk^(k^(2r+1))
1D totalistic rulesk^((k-1)(2r+1)+1)
2D general rulesk^(k^((2r+1)^2))
2D 9-neighbor totalistic rulesk^(9(k-1)+1)
2D 5-neighbor totalistic rulesk^(5(k-1)+1)
2D 5-neighbor outer totalistic rulesk^(k(4(k-1)+1))
  • Normally, all elements in init and the evolution list are integers between 0 and k-1.
  • When a general function or replacement list is used, the elements of init and the evolution list can be any expressions.  »
  • Explicit replacement rules lhsi->rhsi can contain patterns.
  • In a 1D cellular automaton, replacement rules or an explicit function fun are always taken to apply to a 1D list of neighbors. If the neighbors are specified by explicit offsets, they are given in the order of the offsets.
  • When the neighborhood in a multidimensional cellular automaton is defined by a range specification such as {r1, r2, ...}, the list of neighbors is taken to be a full array with dimensions 2{r1, r2, ...}+1.
  • If the neighbors in a multidimensional cellular automaton are specified by an explicit list of offsets, the neighbors are supplied in a one-dimensional list in the order of the offsets.
  • If an explicit function fun is given, the first argument supplied to it is the list of neighbors. The second argument is the step number starting at 0.
  • In an order-s cellular automaton, specified by {rule, kspec, rspec, s}, each step depends on s preceding steps.
  • Initial conditions are constructed from init as follows:
{a1,a2,...}explicit list of values ai, assumed cyclic
{{a1,a2,...},b}values ai superimposed on a b background
{{a1,a2,...},{b1,b2,...}}values ai superimposed on a background of repetitions of b1, b2, ...
{{{{a11,a12,...},off1}, {{a21,...},off2},...},bspec}
values aij at offsets offi on a background
{{a11,a12,...},{a21,...},...}explicit list of values in two dimensions
{aspec,bspec}values in d dimensions with d-dimensional padding
  • The first element of aspec is superimposed on the background at the first position in the positive direction in each coordinate relative to the origin. This means that bspec[[1, 1, ...]] is aligned with aspec[[1, 1, ...]].
  • For an order-s cellular automaton, init is a list giving the initial s steps in the evolution of the system.
  • Time specifications tspec in {tspec, xspec, ...} can be as follows:
tall steps 0 through t
{t}a list containing only step t
{{t}}step t alone
{t1,t2}steps t1 through t2
{t1,t2,dt}steps t1, t1+dt, ...
  • The initial condition is considered to be at step 0.
  • Space specifications xspec can be as follows:
Allall cells that can be affected by the specified initial condition
Automaticall cells in the region that differs from the background
0cell aligned with beginning of aspec
xcells at offsets up to x on the right
-xcells at offsets up to x on the left
{x}cell at offset x to the right
{-x}cell at offset x to the left
{x1,x2}cells at offsets x1 through x2
{x1,x2,dx}cells x1, x1+dx, ...
  • In one dimension, the first element of aspec is taken by default to have space offset 0.
  • In any number of dimensions, aspec[[1, 1, 1, ...]] is taken by default to have space offset {0, 0, 0, ...}.
  • Each element of the evolution list produced by CellularAutomaton is always the same size.
  • With an initial condition specified by an aspec of width w, the region that can be affected after t steps by a cellular automaton with a rule of range r has width w+2rt.
  • If no bspec background is specified, space offsets of All and Automatic will include every cell in aspec.
  • A space offset of All includes all cells that can be affected by the initial condition.
  • A space offset of Automatic can be used to trim off background from the sides of a cellular automaton pattern.
  • In working out how wide a region to keep, Automatic only looks at results on steps specified by offt.
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