Agents Based Modeling (using Agents.jl)

New to Julia
1

I am trying to use Agents.jl package to model my system. I use the following code

using Agents
using LightGraphs
using Distributions

mutable struct MyAgent{T<:Integer,Y<:AbstractFloat} <: AbstractAgent
    id::T ;
    pos::Y ; 
    W::Y ; 
end

mutable struct MyNet{T<:Integer,Y<:AbstractArray} <: AbstractSpace
    dimensions::T ; 
    space::SimpleDiGraph{Int64} ; 
    agent_positions::Y ;
end

mutable struct MyModel{T<:AbstractArray,Y<:AbstractFloat,Z<:AbstractSpace} <: AbstractModel
    space::Z ; 
    agents::T ;
    scheduler::Function ; 
    activation_prob::Y ; 
    interaction_prob::Y ; 
end
function instantiate_model(;num_agents,mean,sd,out_deg,prob_rew,prob_up,prob_int)
    agents = [MyAgent(i,rand(Normal(mean,sd))*pi/180,rand(Uniform(0.5,0.9))) for i in 1:num_agents] ;
    ntwk = MyNet(num_agents,watts_strogatz(num_agents,out_deg,prob_rew,is_directed=true),collect(1:num_agents)) ;
    model = MyModel(ntwk,agents,partial_activation,prob_up,prob_int) ;
    return model
end

function agent_step!(agent::AbstractAgent,model::AbstractModel)
agent.pos = agent.pos + agent[rand].pos ;
end

I want to make sure that the quantities used on the RHS agent[rand].pos are all from [t-1] time step. On using the step!(agent_step!,model) function, this is not possible as everything inside agent_step! gets executed, updated and no exceptions can be made. How can I have a copy of values of agent.pos from [t-1] ?

2

Agents.jl is now in version 2.0, with a massively more simplified API. See Agents.jl : Agent based modelling

1 Like
3

It is a bit late reply. You need to specify a “model_step!” function, instead of an agent_step! to achieve your goal. In a model step function, you define what happens to the model in a single time step. So you can create an array of all agent positions, then update the positions from that array.

The forest fire example in the documentations uses a model step function.

Make sure to check the version 2 of Agents.jl, building the model and collecting data is much simpler now.

1 Like
4

hi, this link no longer works. Could you please resend it…

5

Check this page for all the example models, including forest fire.

1 Like
6

thank you so much. Have you ever tried modelling the vacuum problem in Julia? I am very new to Julia and AI and have no idea how to solve my problem.

7

Hi,

As a newbie for Julia too, and a new user of Agents.jl, I believe it would be beneficial if you tag the question with “agents” under modeling and simulation category, otherwise potential interested members of the community may not be notified.

8

No, not this specific model and I don’t know the problem either. I would read through the tutorial section first. Then if you have specific questions, such as how to write a specific behavior or how to design a specific model, people will be able to help.

1 Like