Agent based models

This page describes functions that can be used in conjunction with Agents.jl to animate and interact with agent based models.

The animation at the start of this page was done by running the examples/daisyworld.jl file, and see also an example application in Agents.jl docs.

InteractiveDynamics.abm_plotFunction
abm_plot(model::ABM; kwargs...) → fig, abmstepper
abm_plot!(ax::Axis/Axis3, model::ABM; kwargs...) → abmstepper

Plot an agent based model by plotting each individual agent as a marker and using the agent's position field as its location on the plot. Requires Agents.

Return the overarching fig object, as well as a struct abmstepper that can be used to interactively animate the evolution of the ABM and combine it with other subplots. The figure is not displayed by default, you need to either return fig as a last statement in your functions or simply call display(fig). Notice that models with DiscreteSpace are plotted starting from 0 to n, with n the space size along each dimension.

To progress the ABM plot n steps simply do:

Agents.step!(abmstepper, model, agent_step!, model_step!, n)

You can still call this function with n=0 to update the plot for a new model, without doing any stepping. From fig you can obtain the plotted axis (to e.g. turn off ticks, etc.) using ax = content(fig[1, 1]). See Sugarscape for an example of using abmstepper to make an animation of evolving the ABM and a heatmap in parallel with only a few lines of code.

Agent related keywords

  • ac, as, am: These three keywords decided the color, size, and marker, that each agent will be plotted as. They can each be either a constant or a function, which takes as an input a single argument and ouputs the corresponding value. For example:

    # ac = "#338c54"
    ac(a) = a.status == :S ? "#2b2b33" : a.status == :I ? "#bf2642" : "#338c54"
    # as = 10
    as(a) = 10*randn() + 1
    # am = :diamond
    am(a) = a.status == :S ? :circle : a.status == :I ? :diamond : :rect

    Notice that for 2D models, am can be/return a Polygon instance, which plots each agent as an arbitrary polygon. It is assumed that the origin (0, 0) is the agent's position when creating the polygon. In this case, the keyword as is meaningless, as each polygon has its own size. Use the functions scale, rotate2D to transform this polygon.

    3D models currently do not support having different markers. As a result, am cannot be a function. It should be a Mesh or 3D primitive (such as Sphere or Rect3D).

  • scheduler = model.scheduler: decides the plotting order of agents (which matters only if there is overlap).

  • offset = nothing: If not nothing, it must be a function taking as an input an agent and outputting an offset position tuple to be added to the agent's position (which matters only if there is overlap).

  • scatterkwargs = (): Additional keyword arguments propagated to the scatter! call.

Preplot related keywords

  • heatarray = nothing : A keyword that plots a heatmap over the space. Its values can be standard data accessors given to functions like run!, i.e. either a symbol (directly obtain model property) or a function of the model. The returned data must be a matrix of the same size as the underlying space. For example heatarray = :temperature is used in the Daisyworld example. But you could also define f(model) = create_some_matrix_from_model... and set heatarray = f. The heatmap will be updated automatically during model evolution in videos and interactive applications.
  • heatkwargs = NamedTuple() : Keywords given to Makie.heatmap function if heatarray is not nothing.
  • static_preplot! : A function f(ax, model) that plots something after the heatmap but before the agents. Notice that you can still make objects of this plot be visible above the agents using a translation in the third dimension like below:
    function static_preplot!(ax, model)
        obj = scatter!(ax, [50 50]; color = :red) # Show position of teacher
        hidedecorations!(ax) # hide tick labels etc.
        translate!(obj, 0, 0, 5) # be sure that the teacher will be above students
    end

Figure related keywords

These only matter for abm_plot and not for abm_plot!.

  • resolution = (600, 600): Resolution of the figure.
  • backgroundcolor = DEFAULT_BG: Background color of the figure.
  • axiskwargs = NamedTuple(): Keyword arguments given to the main axis creation for e.g. setting xticksvisible = false.
  • aspect = DataAspect(): The aspect ratio behavior of the axis.
source
InteractiveDynamics.abm_playFunction
abm_play(model, agent_step! [, model_step!]; kwargs...) → fig, abmstepper

Launch an interactive application that plots an agent based model and can animate its evolution in real time. Requires Agents.

The agents are plotted exactly like in abm_plot, while the two functions agent_step!, model_step! decide how the model will evolve, as in the standard approach of Agents.jl and its step! function.

The application has three buttons:

  • "step": advances the simulation once for spu steps.
  • "run": starts/stops the continuous evolution of the model.
  • "reset": resets the model to its original configuration.

Two sliders control the animation speed: "spu" decides how many model steps should be done before the plot is updated, and "sleep" the sleep() time between updates.

Keywords

  • ac, am, as, scheduler, offset, aspect, scatterkwargs: propagated to abm_plot.
  • spu = 1:100: The values of the "spu" slider.
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InteractiveDynamics.abm_videoFunction
abm_video(file, model, agent_step! [, model_step!]; kwargs...)

This function exports the animated time evolution of an agent based model into a video saved at given path file, by recording the behavior of abm_play (without sliders). The plotting is identical as in abm_plot and applicable keywords are propagated.

Keywords

  • spf = 1: Steps-per-frame, i.e. how many times to step the model before recording a new frame.
  • framerate = 30: The frame rate of the exported video.
  • frames = 300: How many frames to record in total, including the starting frame.
  • title = "": The title of the figure.
  • showstep = true: If current step should be shown in title.
  • kwargs...: All other keywords are propagated to abm_plot.
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InteractiveDynamics.abm_data_explorationFunction
abm_data_exploration(model::ABM, agent_step!, model_step!, params=Dict(); kwargs...)

Open an interactive application for exploring an agent based model and the impact of changing parameters on the time evolution. Requires Agents.

The application evolves an ABM interactively and plots its evolution, while allowing changing any of the model parameters interactively and also showing the evolution of collected data over time (if any are asked for, see below). The agent based model is plotted and animated exactly as in abm_play, and the arguments model, agent_step!, model_step! are propagated there as-is.

Calling abm_data_exploration returns: fig, agent_df, model_df. So you can save the figure, but you can also access the collected data (if any).

Interaction

Besides the basic time evolution interaction of abm_play, additional functionality here allows changing model parameters in real time, based on the provided fourth argument params. This is a dictionary which decides which parameters of the model will be configurable from the interactive application. Each entry of params is a pair of Symbol to an AbstractVector, and provides a range of possible values for the parameter named after the given symbol (see example online). Changing a value in the parameter slides is only updated into the actual model when pressing the "update" button.

The "reset" button resets the model to its original agent and space state but it updates it to the currently selected parameter values. A red vertical line is displayed in the data plots when resetting, for visual guidance.

Keywords

  • ac, am, as, scheduler, offset, aspect, scatterkwargs: propagated to abm_plot.
  • adata, mdata: Same as the keyword arguments of Agents.run!, and decide which data of the model/agents will be collected and plotted below the interactive plot. Notice that data collection can only occur on plotted steps (and thus steps not plotted due to "spu" are also not data-collected).
  • alabels, mlabels: If data are collected from agents or the model with adata, mdata, the corresponding plots have a y-label named after the collected data. Instead, you can give alabels, mlabels (vectors of strings with exactly same length as adata, mdata), and these labels will be used instead.
  • when = true: When to perform data collection, as in Agents.run!.
  • spu = 1:100: Values that the "spu" slider will obtain.
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Agent inspection

It is possible to inspect agents at a given position by hovering the mouse cursor over the scatter points in the agent plot. A tooltip will appear which by default provides the name of the agent type, its id, pos, and all other fieldnames together with their current values. This is especially useful for interactive exploration of micro data on the agent level.

For this functionality, we draw on the powerful features of Makie's DataInspector.

The tooltip can be customized both with regards to its content and its style by extending a single function and creating a specialized method for a given A<:AbstractAgent.

InteractiveDynamics.agent2stringFunction
agent2string(agent::A)

Convert agent data into a string which is used to display all agent variables and their values in the tooltip on mouse hover. Concatenates strings if there are multiple agents at one position.

Custom tooltips for agents can be implemented by adding a specialised method for agent2string.

Example:

function InteractiveDynamics.agent2string(agent::SpecialAgent)
    """
    ✨ SpecialAgent ✨
    ID = $(agent.id)
    Main weapon = $(agent.charisma)
    Side weapon = $(agent.pistol)
    """
end
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Adding custom plots

Tracking model variables is already made easy by adding them to the adata/mdata vectors.

using Agents
using Statistics
using InteractiveDynamics
using GLMakie

# initialise model
model, agent_step!, model_step! = Models.schelling()

# define a parameter slider
params = Dict(:min_to_be_happy => 1:1:5)

# define data to collect and plot
adata= [(:mood, mean)]

# open the interactive app
fig, adf, mdf = abm_data_exploration(model, agent_step!, model_step!, params; adata)
Regular interactive app for data exploration

This will always display the data as scatterpoints connected with lines. In cases where more granular control over the displayed plots is needed, we need to take a few extra steps. Makie plots have to know which changes in the underlying data to watch. This is done by using Observables. We can simply add the variable in question as an Observable and update it after each simulation step. This can be done by adding a new stepping function which wraps the original model_step! function and the updating of the Observable's value.

For the sake of a simple example, let's assume we want to add a barplot showing the current amount of happy and unhappy agents in our Schelling segregation model.

# add the new variable as an observable
happiness = [count(a.mood == false for a in allagents(model)),
    count(a.mood == true for a in allagents(model))] |> Observable

# update its value after each model step
function new_model_step!(model; happiness = happiness)
    model_step!(model)
    happiness[] = [count(a.mood == false for a in allagents(model)),
        count(a.mood == true for a in allagents(model))]
end

# open the interactive app and use the enhanced stepping function as an argument
fig, adf, mdf = abm_data_exploration(model, agent_step!, new_model_step!, params; adata)

# add the desired plot to a newly created column on the right
barplot(fig[:,3], [0,1], happiness; bar_labels = ["Unhappy", "Happy"])

# as usual, we can also style this new plot to our liking
hidexdecorations!(current_axis())