MTH108: HOMEWORK 6 – CELLULAR AUTOMATA
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MTH108: HOMEWORK 6 – CELLULAR AUTOMATA
Please attempt sections A and B before the tutorials.
Section A – Warm-up questions
A1. Given n, k ∈ N, what is the total number of configurations for cellular automaton on a universe of n cells and an alphabet of k elements?
A2. Draw the set of T-shaped dominoes that define the elementary cellular automaton Rule 158.
Section B – Main questions
B1. Iterate the elementary cellular automaton Rule 22 for 5 generations, taking an initial condition with exactly one black cell .
B2. In Conway’s Game of Life, a configuration of only four live cells arranged adjacently in a square is an equilibrium: it does not change from one generation to the next . Find equilibrium configurations consisting of exactly n live cells, for n = 5, 6, 7, 8 cells .
B3. (Forest Fire) Suppose that we model the spread of a forest fire over the first few hours using a cellular automaton on a 2-dimensional grid z2 . Suppose that each cell has two states 1 (fire) and 0 (no fire) . We assume that if a cell is on fire, then if will still be on fire one hour later . Because of the prevailing wind direction in the region, a cell with no fire will have fire one hour later if the cell to the west or north-west is
on fire, otherwise a cell without fire will still have no fire one hour later . Suppose that the fire begins in two adjacent cells . How will the number of cells on fire change over the subsequent hours? Is there a formula for the number of cells on fire after n hours?
B4. (Algal dispersion) Suppose that a species of algae is introduced to the bank of a lake . Suppose that the algae begin to spread around the edge of the lake from one month to the next . Let us model the situation with elementary cellular automoton Rule 126 implemented on a finite cyclic universe consisting of n cells arranged in a loop . Investigate the behaviour of the solution for n = 9, 10, 11.
B5. (Yeast growth) Suppose that we model the growth of a species of yeast across a surface on a lattice of regular hexagonal cells . Suppose that each cell has two states 1 (yeast) and 0 (no yeast) . A cell with no yeast will gain yeast one hour later if two or more of its six neighbours have yeast, otherwise the state of a cell does not change . Suppose that the initial state only has yeast in two adjacent cells . How many cells will have yeast over the next 5 hours?
Section C – Investigations
C1. (Surjectivity) Consider the elementary cellular automaton Rule 90. Show that every configuration has four predecessors . Find the four predecessors for the configuration with one black cell .
C2. (Garden of Eden) A garden of Eden is a configuration that can only occur as an initial condition: it has no predecessor . Find an elementary cellular automaton with a garden of Eden .
2023-04-21