SSC2018 introduction to agent-based modeling in Julia

forestfire1.jl

using Random

function setup(density)
    [x == 1 ? 2 : rand() < density ? 1 : 0 for x in 1:251, y in 1:251]
end

function go(grid)
    any(isequal(2), grid) || return true
    for pos in shuffle!(findall(isequal(2), grid))
        x, y = pos[1], pos[2]
        for (dx, dy) in ((0, 1), (0, -1), (1, 0), (-1, 0))
            nx, ny = x + dx, y + dy
            if all((0,0) .< (nx, ny) .≤ size(grid)) && grid[nx, ny] == 1
                grid[nx, ny] = 2
            end
        end
        grid[pos] = 3
    end
    return false
end

function go_repeat(density)
    grid = setup(density)
    init_green = count(isequal(1), grid)
    while true
        go(grid) && return count(isequal(3), grid) / init_green * 100
    end
end

@time [go_repeat(0.55) for i in 1:100];
@time [go_repeat(0.75) for i in 1:100];

forestfire2.jl

using Random

mutable struct Tree
    state::Symbol
    when::Int

    Tree(state, when=0) = new(state, when)
end

function setup(density)
    [Tree(x == 1 ? :red : rand() < density ? :green : :black) for x in 1:251, y in 1:251]
end

function go(grid, tick)
    any(t -> t.state == :red, grid) || return true
    for pos in shuffle!(findall(t -> t.state == :red, grid))
        x, y = pos[1], pos[2]
        for (dx, dy) in ((0, 1), (0, -1), (1, 0), (-1, 0))
            nx, ny = x + dx, y + dy
            if all((0,0) .< (nx, ny) .≤ size(grid)) && grid[nx, ny].state == :green
                grid[nx, ny].state = :red
            end
        end
        grid[pos].state = :brown
        grid[pos].when = tick
    end
    return false
end

function go_repeat(density)
    grid = setup(density)
    init_green = count(t -> t.state == :green, grid)
    tick = 1
    while true
        go(grid, tick) && return count(t -> t.state == :brown, grid) / init_green * 100
        tick += 1
    end
end

@time [go_repeat(0.55) for i in 1:100];
@time [go_repeat(0.75) for i in 1:100];

forestfire3.jl

using Random

struct TreeGreen
end

struct TreeRed
end

struct TreeBrown
    when::Int
end

function setup(density)
    [x == 1 ? TreeRed() : rand() < density ?
              TreeGreen() : nothing for x in 1:251, y in 1:251]
end

function go(grid, tick)
    any(isequal(TreeRed()), grid) || return true
    for pos in shuffle!(findall(isequal(TreeRed()), grid))
        x, y = pos[1], pos[2]
        for (dx, dy) in ((0, 1), (0, -1), (1, 0), (-1, 0))
            nx, ny = x + dx, y + dy
            if all((0,0) .< (nx, ny) .≤ size(grid)) && grid[nx, ny] isa TreeGreen
                grid[nx, ny] = TreeRed()
            end
        end
        grid[pos] = TreeBrown(tick)
    end
    return false
end

function go_repeat(density)
    grid = setup(density)
    init_green = count(isequal(TreeGreen()), grid)
    tick = 1
    while true
        go(grid, tick) && return count(t -> t isa TreeBrown, grid) / init_green * 100
        tick += 1
    end
end

@time [go_repeat(0.55) for i in 1:100];
@time [go_repeat(0.75) for i in 1:100];

forestfire4.jl

using Random

struct TreeID
    typ::Int
    loc::Int
end

struct TreeGreen
end

struct TreeRed
    x::Int
    y::Int
end

struct TreeBrown
    when::Int
end

function setup(density)
    trees = (TreeGreen[], TreeRed[], TreeBrown[])
    grid = Matrix{TreeID}(undef, 251, 251)
    for x in axes(grid, 1), y in axes(grid, 2)
        if x == 1
            push!(trees[2], TreeRed(x, y))
            grid[x, y] = TreeID(2, length(trees[2]))
        elseif rand() < density
            push!(trees[1], TreeGreen())
            grid[x, y] = TreeID(1, length(trees[1]))
        else
            grid[x, y] = TreeID(0, 0)
        end
    end
    grid, trees
end

function burn(t, grid, trees, tick)
    for (dx, dy) in ((0, 1), (0, -1), (1, 0), (-1, 0))
        nx, ny = t.x + dx, t.y + dy
        if all((0,0) .< (nx, ny) .≤ size(grid)) && grid[nx, ny].typ == 1
            push!(trees[2], TreeRed(nx, ny))
            grid[nx, ny] = TreeID(2, length(trees[2]))
        end
    end
    push!(trees[3], TreeBrown(tick))
    grid[t.x, t.y] = TreeID(3, length(trees[3]))
end

function go(grid, trees, tick)
    any(t -> t.typ == 2, grid) || return true
    for pos in shuffle!(findall(t -> t.typ == 2, grid))
        burn(trees[2][grid[pos].loc], grid, trees, tick)
    end
    return false
end

function go_repeat(density)
    grid, trees = setup(density)
    init_green = count(t -> t.typ == 1, grid)
    tick = 1
    while true
        go(grid, trees, tick) && return count(t -> t.typ == 3, grid) / init_green * 100
        tick += 1
    end
end

@time [go_repeat(0.55) for i in 1:100];
@time [go_repeat(0.75) for i in 1:100];