The CarryDrop Model (Steps 4-9) : A RePast Tutorial by John Murphy

1
The CarryDrop Model (Steps 4-9) A RePast
Tutorial by John Murphy

• by Junjie Sun
• 8/2/2004
• Department of Economics
• Iowa State University

2
Review of the Story

• Agents move around a grid space
• Move in one of the eight directions
• Each cell may contain money agents pick it up
  and carry it with them
• Collision compensation then the agent chooses a
  new direction
• Agent has lifespan when agent dies, its wealth
  is spread randomly onto the grid, and the dead
  agent is replaced with a newly born in a diff.
  location with a diff. lifespan

3
Review of Model Structure

• CarryDropModel - a class that instantiates the
  SimModel object
• CarryDropAgent - a class specifying the agents
• CarryDropSpace - a class describing the space

4
Whats been done in Step 1-3

• CarryDropModel
• Variables schedule, numAgents
• Methods setup(), begin(), buildModel(),
  buildSchedule(), buildDisplay(), getName(),
  getSchedule(), getInitParam(), getNumAgents(),
  setNumAgents(), main()
• CarryDropAgent
• CarryDropSpace

5
Add User-Settable Parameters (Step 4-1)

• Number of Agents (NumAgents)
• Size of World X (WorldXSize)
• Size of World Y (WorldYSize)

6
Add User-Settable Parameters (Step 4-2)

• Add worldXSize worldYSize as class variables
• private int worldXSize
• private int worldYSize
• Add WorldXSize WorldYSize to the getInitParam
  function
• String initParams "NumAgents" ,
  "WorldXSize", "WorldYSize"
• Add the get and set methods for these variables,
  for example,
• public int getWorldXSize()
• return worldXSize

7
Compiling and Running the Basic Model (Step 5-1)

• Create a new project in IDE and add in three
  .java files, namely, CarryDropModel.java
  CarryDropAgent.java CarryDropSpace.java
• The model wont do anything, but it should
  compile and display part of the RePast GUI

8
Codes to be Added in main Method (Step 5-2)

• Creates a new obj. of type SimInit
• SimInit init new SimInit()
• Creates a new object of type CarryDropModel
• CarryDropModel model new CarryDropModel()
• Loads the model using the loadModel method of the
  Init obj.
• init.loadModel(model, "", false)

9
Default Values for User-Settable Parameters (Step
6)

• private static final int NUMAGENTS 100
• private static final int WORLDXSIZE 40
• private static final int WORLDYSIZE 40
• private int numAgents NUMAGENTS
• private int worldXSize WORLDXSIZE
• private int worldYSize WORLDYSIZE

10
Alerts in Subroutines (Step 7)

• System.out.println("Running setup")
• System.out.println("Running BuildModel")
• System.out.println("Running BuildSchedule")
• System.out.println("Running BuildDisplay")

11
The Space Object (Step 8-1)

• Define the variable for space object using
  RePasts Object2DGrid
• private Object2DGrid moneySpace
• Fill moneySpace with Integer objects
• public CarryDropSpace(int xSize, int ySize)
• moneySpace new Object2DGrid(xSize,
  ySize)
• for(int i 0 i lt xSize i)
• for(int j 0 j lt ySize j)
• moneySpace.putObjectAt(i,j,new
  Integer(0))

12
Q How can you know the args in the methods /
constructors? A See RePast/Java API (Step 8-2)

• Object2DGrid(int xSize, int ySize) 
• Constructs a grid with the specified size.
• Integer(int value)
• Constructs a newly allocated Integer object that
  represents the primitive int argument.
• putObjectAt(int x, int y, Object object)
• Puts the specified object at (x,y)

13
Need another parameter, the amount of money (Step
8-3)

• In CarryDropModel.java, add
• private static final int TOTALMONEY 1000
• private int money TOTALMONEY
• String initParams "NumAgents" ,
  "WorldXSize", "WorldYSize", "Money"
• public int getMoney() return money
• public void setMoney(int i) money i

14
Integrate the Space Object into the Model (Step
9-1)

• Allocate a variable for the space object
• private CarryDropSpace cdSpace
• Create the space object in buildModel()
• cdSpace new CarryDropSpace (worldXSize,
  worldYSize)
• Destroy the space object in setup()
• cdSpace null

15
Some Clarifications (Step 9-2)

• The space object is actually destroyed (set to
  null) in setup before it is created in the
  buildModel
• Reason is that in each simulation run, the object
  needs to be reset to nothing before it gets ready
  to be built

16
Overview Whats been done in Step 1-9

• CarryDropModel
• Variables schedule, cdSpace, numAgents,
  worldXSize, worldYSize, money
• Methods setup(), begin(), buildModel(),
  buildSchedule(), buildDisplay(), getName(),
  getSchedule(), getInitParam(), getNumAgents(),
  setNumAgents(), getWorldXSize(), setWorldXSize(),
  getWorldYSize(), setWorldYSize(), getMoney(),
  setMoney(), main()
• CarryDropAgent
• CarryDropSpace
• Variables moneySpace
• Constructors CarryDropSpace()