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‎docs/src/lecture_02/hw.md‎

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# Homework 2: Predator-Prey Agents
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In this lab you will continue working on your agent simulation. If you did not
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manage to finish the homework, do not worry, you can use the code below which
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contains all the functionality we developed in the lab.
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```@raw html
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<details class = "solution-body">
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<summary class = "solution-header">Solution of Lab 2:</summary><p>
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manage to finish the homework, do not worry, you can use [this
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script](https://github.com/JuliaTeachingCTU/Scientific-Programming-in-Julia/blob/master/src/Lab02Ecosystem.jl)
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which contains all the functionality we developed in the lab.
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```@setup hw02
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projdir = dirname(Base.active_project())
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include(joinpath(projdir,"..","src","Lab02Ecosystem.jl"))
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```
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```@example hw02
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using StatsBase
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abstract type Agent end
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abstract type Animal <: Agent end
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abstract type Plant <: Agent end
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## How to submit?
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mutable struct World{A<:Agent}
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agents::Dict{Int,A}
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max_id::Int
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end
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function World(agents::Vector{<:Agent})
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World(Dict(id(a)=>a for a in agents), maximum(id.(agents)))
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end
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Put all your code (including your or the provided solution of lab 2) in a
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script named `hw.jl` alongside with the `Project.toml` and `Manifest.toml` of
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the environment. Please only include packages in the environment that are
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necessary for the homework. Create a `.zip` archive of the three files and
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send it to the lab instructor, who has assigned the task, via email (contact
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emails are located on the [homepage](@ref emails) of the course).
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# optional: you can overload the `show` method to get custom
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# printing of your World
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function Base.show(io::IO, w::World)
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println(io, typeof(w))
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for (_,a) in w.agents
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println(io," $a")
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end
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end
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function world_step!(world::World)
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# make sure that we only iterate over IDs that already exist in the
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# current timestep this lets us safely add agents
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ids = deepcopy(keys(world.agents))
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for id in ids
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# agents can be killed by other agents, so make sure that we are
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# not stepping dead agents forward
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!haskey(world.agents,id) && continue
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a = world.agents[id]
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agent_step!(a,world)
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end
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end
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function agent_step!(a::Plant, w::World)
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if size(a) != max_size(a)
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grow!(a)
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end
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end
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function agent_step!(a::Animal, w::World)
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incr_energy!(a,-1)
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if rand() <= foodprob(a)
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dinner = find_food(a,w)
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eat!(a, dinner, w)
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end
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if energy(a) <= 0
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kill_agent!(a,w)
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return
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end
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if rand() <= reprprob(a)
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reproduce!(a,w)
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end
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return a
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end
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mutable struct Grass <: Plant
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id::Int
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size::Int
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max_size::Int
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end
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mutable struct Sheep <: Animal
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id::Int
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energy::Float64
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Δenergy::Float64
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reprprob::Float64
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foodprob::Float64
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end
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mutable struct Wolf <: Animal
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id::Int
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energy::Float64
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Δenergy::Float64
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reprprob::Float64
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foodprob::Float64
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end
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id(a::Agent) = a.id # every agent has an ID so we can just define id for Agent here
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Base.size(a::Plant) = a.size
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max_size(a::Plant) = a.max_size
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grow!(a::Plant) = a.size += 1
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# get field values
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energy(a::Animal) = a.energy
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Δenergy(a::Animal) = a.Δenergy
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reprprob(a::Animal) = a.reprprob
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foodprob(a::Animal) = a.foodprob
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# set field values
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energy!(a::Animal, e) = a.energy = e
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incr_energy!(a::Animal, Δe) = energy!(a, energy(a)+Δe)
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function eat!(a::Sheep, b::Grass, w::World)
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incr_energy!(a, size(b)*Δenergy(a))
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kill_agent!(b,w)
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end
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function eat!(wolf::Wolf, sheep::Sheep, w::World)
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incr_energy!(wolf, energy(sheep)*Δenergy(wolf))
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kill_agent!(sheep,w)
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end
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eat!(a::Animal,b::Nothing,w::World) = nothing
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kill_agent!(a::Plant, w::World) = a.size = 0
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kill_agent!(a::Animal, w::World) = delete!(w.agents, id(a))
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function find_food(a::Animal, w::World)
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as = filter(x->eats(a,x), w.agents |> values |> collect)
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isempty(as) ? nothing : sample(as)
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end
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eats(::Sheep,::Grass) = true
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eats(::Wolf,::Sheep) = true
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eats(::Agent,::Agent) = false
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function reproduce!(a::A, w::World) where A<:Animal
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energy!(a, energy(a)/2)
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a_vals = [getproperty(a,n) for n in fieldnames(A) if n!=:id]
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new_id = w.max_id + 1
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â = A(new_id, a_vals...)
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w.agents[id(â)] = â
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w.max_id = new_id
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end
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nothing # hide
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```
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```@raw html
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</p></details>
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```
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## Counting Agents
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```@raw html
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<div class="admonition is-category-homework">
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<header class="admonition-header">Homework (2 points)</header>
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<header class="admonition-header">Compulsory Homework (2 points)</header>
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<div class="admonition-body">
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```
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1. Implement a function `agent_count` that can be called on a single
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```@repl hw02
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grass1 = Grass(1,5,5);
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agent_count(grass1)
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grass2 = Grass(2,1,5);
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agent_count([grass1,grass2]) # one grass is fully grown; the other only 20% => 1.2
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sheep = Sheep(3,10.0,5.0,1.0,1.0);
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wolf = Wolf(4,20.0,10.0,1.0,1.0);
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world = World([grass1, grass2, sheep, wolf]);
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agent_count(world) # one grass is fully grown; the other only 20% => 1.2
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agent_count(world)
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```
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Hint: You can get the *name* of a type by using the `nameof` function:
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```@raw html
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<div class="admonition is-category-exercise">
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<header class="admonition-header">Exercise (voluntary)</header>
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<header class="admonition-header">Voluntary Exercise (voluntary)</header>
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<div class="admonition-body">
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```
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Using the world below, run few `world_step!`s. Plot trajectories of the agents

‎src/Lab02Ecosystem.jl‎

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Original file line numberDiff line numberDiff line change
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using StatsBase
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abstract type Agent end
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abstract type Animal <: Agent end
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abstract type Plant <: Agent end
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mutable struct World{A<:Agent}
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agents::Dict{Int,A}
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max_id::Int
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end
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function World(agents::Vector{<:Agent})
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World(Dict(id(a)=>a for a in agents), maximum(id.(agents)))
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end
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# optional: you can overload the `show` method to get custom
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# printing of your World
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function Base.show(io::IO, w::World)
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println(io, typeof(w))
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for (_,a) in w.agents
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println(io," $a")
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end
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end
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function world_step!(world::World)
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# make sure that we only iterate over IDs that already exist in the
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# current timestep this lets us safely add agents
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ids = deepcopy(keys(world.agents))
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for id in ids
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# agents can be killed by other agents, so make sure that we are
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# not stepping dead agents forward
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!haskey(world.agents,id) && continue
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a = world.agents[id]
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agent_step!(a,world)
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end
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end
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function agent_step!(a::Plant, w::World)
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if size(a) != max_size(a)
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grow!(a)
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end
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end
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function agent_step!(a::Animal, w::World)
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incr_energy!(a,-1)
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if rand() <= food_prob(a)
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dinner = find_food(a,w)
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eat!(a, dinner, w)
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end
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if energy(a) <= 0
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kill_agent!(a,w)
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return
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end
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if rand() <= reproduction_prob(a)
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reproduce!(a,w)
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end
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return a
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end
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mutable struct Grass <: Plant
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id::Int
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size::Int
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max_size::Int
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end
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mutable struct Sheep <: Animal
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id::Int
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energy::Float64
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Δenergy::Float64
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reproduction_prob::Float64
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food_prob::Float64
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end
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mutable struct Wolf <: Animal
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id::Int
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energy::Float64
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Δenergy::Float64
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reproduction_prob::Float64
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food_prob::Float64
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end
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id(a::Agent) = a.id # every agent has an ID so we can just define id for Agent here
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Base.size(a::Plant) = a.size
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max_size(a::Plant) = a.max_size
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grow!(a::Plant) = a.size += 1
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# get field values
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energy(a::Animal) = a.energy
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Δenergy(a::Animal) = a.Δenergy
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reproduction_prob(a::Animal) = a.reproduction_prob
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food_prob(a::Animal) = a.food_prob
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# set field values
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energy!(a::Animal, e) = a.energy = e
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incr_energy!(a::Animal, Δe) = energy!(a, energy(a)+Δe)
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function eat!(a::Sheep, b::Grass, w::World)
100+
incr_energy!(a, size(b)*Δenergy(a))
101+
kill_agent!(b,w)
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end
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function eat!(wolf::Wolf, sheep::Sheep, w::World)
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incr_energy!(wolf, energy(sheep)*Δenergy(wolf))
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kill_agent!(sheep,w)
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end
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eat!(a::Animal,b::Nothing,w::World) = nothing
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kill_agent!(a::Plant, w::World) = a.size = 0
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kill_agent!(a::Animal, w::World) = delete!(w.agents, id(a))
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function find_food(a::Animal, w::World)
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as = filter(x->eats(a,x), w.agents |> values |> collect)
114+
isempty(as) ? nothing : sample(as)
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end
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eats(::Sheep,::Grass) = true
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eats(::Wolf,::Sheep) = true
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eats(::Agent,::Agent) = false
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function reproduce!(a::A, w::World) where A<:Animal
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energy!(a, energy(a)/2)
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a_vals = [getproperty(a,n) for n in fieldnames(A) if n!=:id]
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new_id = w.max_id + 1
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â = A(new_id, a_vals...)
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w.agents[id(â)] = â
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w.max_id = new_id
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end

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