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4. Epidemic Model

View this tutorial on Google Docs external link

You will create an epidemic model that simulates the spread of a disease through a population.

Prerequisites​

  • Navigate to profile, create/rename projects
  • Create turtle agents and give them different traits (color/shape)
  • Switch between Pages
  • Reset the simulation: deleting old turtle agents before creating new ones
  • Scatter turtle agents

Learning Objectives​

  • Describe how to use the "random___" block to assign a trait to a portion of the agent populations and in movement
  • Form conditional expressions using comparison operators and "If___" blocks
  • Give an example of a trait dependent collision and explain how these are programmed
  • Explain how the model accurately simulates an epidemic model
  • Construct a line graph of healthy and infected turtle agents

New Terms​

Random

New Blocks​

Random___ • With _ % chance

Overview​

To construct this model, you will need to:

  1. Create turtle agents in the world.
  2. Make some of those turtle agents sick.
  3. Make the turtle agents move.
  4. Make the disease spread via collision.
  5. Make a line graph that displays the count of sick and healthy turtle agents.
  6. Make the turtle agents recover.
  7. Expand the model and make it your own!

Part 1: Create Healthy Agents​

Goal: Create 300 yellow agents which represent the "healthy" population

Steps​

  • Create a new blank project and rename the project to "Epidemic (Your username)"
  • On The World page, create 300 Turtle agents when "setup" is pushed
  • Set the agent's color to yellow and shape to sphere
  • Scatter all agents when "setup" is pushed
  • Delete all old agents when "setup" is pushed

Helpful Coding Blocks​

BlockDrawerUse
when pushed blockInterfaceExecutes the code within the block when a Push Button widget is pushed.
create each do blockAgentsCreates a certain number of agents, and each agent executes the commands within the block.
delete everyone blockAgentsDeletes all agents from The World.
set my to blockTraitsSets a certain trait of an agent to another value.
scatter blockAgentsPlaces an agent in a random location within The World.

Check your Progress!​

Click run code and setup. You should see 300 agents scattered around SpaceLand.

300 yellow agents scattered
Show Solution
Part 1 solution code

Part 2: Create Sick Agents​

Goal: Create 5 red agents who represent the "sick" population

Steps​

  • On The World page, create 5 agents who are "sick" when setup is pushed (use same "when pushed _" as previous step)
    • Have this be indicated by the color red.
    • Set the agent's shape to sphere
  • Scatter them

Helpful Coding Blocks​

BlockDrawerUse
create each do blockAgentsCreates a certain number of agents, and each agent executes the commands within the block.
set my to blockTraitsSets a certain trait of an agent to another value.
scatter blockAgentsPlaces an agent in a random location within The World.
color blockTraitsCreates the specified color.

Check your Progress!​

Click run code and setup. You should see 300 yellow agents and five red agents scattered around SpaceLand.

300 yellow and 5 red agents
Show Solution
Part 2 solution code

Part 3: Make the Agents Move​

Goal: Make the agents randomly move around SpaceLand

Steps​

  • On Turtle page, while forever is toggled on have the agent:
    • Move forward 1
    • Move random left between 0 and 10 degrees
    • Random right between 0 and 10 degrees

Helpful Coding Blocks​

BlockDrawerUse
while toggled blockInterfaceExecutes the code within the block when a Toggle Button widget is on.
forward blockMovementMoves the agent forward a certain value.
left by degs blockMovementTurns left with a set number of degrees during each tick.
right by degs blockMovementTurns right with a set number of degrees during each tick.
random to blockMathRandom _ to _ returns an integer between the two values, inclusive. Generates a new random number each time.

Check your Progress!​

Click run code, setup, and forever. You should see the Turtle agents move in a random path around SpaceLand.

Show Solution
Part 3 solution code

Part 4: Make the Disease Spread​

Goal: Program a collision to simulate the spread of the disease by having "healthy" agents turn red when they collide with a "sick" agent

Steps​

  • On Turtle page, program a collision where:
    • If I (the collider) am yellow and the other agent (collidee) is red, then change my color to red

Helpful Coding Blocks​

BlockDrawerUse
on collision with blockDetectionCarries out code when an agent collides with another object of choice.
set my to blockTraitsSets a certain trait of an agent to another value.
collidee blockDetectionRefers to the object that collides into the agent.
trait of blockTraitsReturns the value of a trait belonging to another agent (such as collidee or my parent).
if blockLogicCarries out the code within the block if the condition is fulfilled.
equals blockLogicDetermines whether the two inputs are equivalent and returns true or false.

Check your Progress!​

Click run code, setup, and forever. You should see yellow agents turn red as they collide with each other.

Disease spreading
Show Solution
Part 4 solution code

Part 5: Make a Line Graph to Display Each Population​

Goal: Create a line graph widget that counts each population and clear the graph when "setup" is pushed

Steps​

  • In "edit interface" mode:
    • Add a line graph widget to SpaceLand and name it "Population"
    • Create two series -- "# of healthy turtles" and "# of sick turtles"
  • On The World page, while forever is toggled:
    • Have "Population" graph update the "# of healthy turtles" series by counting the amount of yellow agents within SpaceLand
      • Make the x-axis the clock and the y-axis "# of healthy turtles"
    • Do the same for the "# of sick turtles" series and have it count red agents
  • Program that when "setup" is pushed the clock is set to 0 and the line graph is cleared

Helpful Coding Blocks​

BlockDrawerUse
add data to line graph blockInterfaceAdds data that's made up of pairs of x-coordinates and y-coordinates.
count within steps blockDetectionCounts the number of agents of a specific breed in a given radius with a specific trait. Use 200 steps to cover the entire terrain.
color blockTraitsRepresents a specific color or a color at random chosen from the drop down menu.
clock blockEnvironmentReturns the value of the clock, measured in "ticks".
set clock to blockEnvironmentSets the value of clock to some number. Typically, when you reset the clock, you want to start it at 0.
clear line graph blockInterfaceRemoves the existing data on the graph.

Check your Progress!​

Click Run Code, setup, and forever. You should see the line graph updating.

Population line graph
Show Solution

Setup code (The World page):

Part 5 setup solution

Graph update code (The World page):

Part 5 graph solution

Part 6: Make the Agents Recover​

Goal: Program the red agents to have a low chance to change color to blue

Steps​

  • On the turtle page, in the existing "while _ is toggled" block:
    • Program that if an agent is red they have a 5% chance of their color becoming blue
      • Blue now represents "immunity" to the disease

Helpful Coding Blocks​

BlockDrawerUse
set my to blockTraitsSets a certain trait of an agent to another value.
color blockTraitsRepresents a specific color or a color at random chosen from the drop down menu.
my blockTraitsRefers to an agent's own trait.
if blockLogicCarries out the code within the block if the condition is fulfilled.
equals blockLogicDetermines whether the two inputs are equivalent and returns true or false.
with % chance blockLogicRuns the commands attached to the hook randomly with a certain percent chance each time the block is run.

Check your Progress!​

Click run code, setup, and forever. You should see red agents change their color to blue.

Show Solution
Part 6 solution code

Part 7: Extensions​

Come up with a question to investigate or just tinker with the existing model. Note that the suggestions in the list below tend to progress from easier tasks to harder tasks. Some of them also require you to learn to use new blocks that haven't been introduced yet. You are also welcome to come up with your own extensions and just explore/try things on your own.

  • Change set up conditions: % immune, % infected
  • Change recovery probability -- e.g., how does lowering it (turtles take longer to recover) affect the spread of the disease?
  • Represent masking or handwashing: during a collision with a sick turtle agent, program there to be a reduced chance that a healthy turtle agent will get sick.
  • Vary the recovery probability -- perhaps some percentage of the population recovers quickly while others take longer to recover.
  • Vary how likely a turtle will get sick -- perhaps some percentage of the population are more susceptible than others.
  • Add a vaccination center (new breed) that makes turtles immune when they collide with it. Do all turtles need to be vaccinated to stop the spread of the disease?
  • Add doctors (new breed) that can "cure" sick turtles. If you've already done Paintball, you can program keyboard controls to move one of the doctors and to "shoot" vaccines at turtles.
  • Which factor seems to slow the spread of the disease the best?

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