A RePast Tutorial by John T. Murphy, University of Arizona & Arizona State University (contact)

The CarryDrop model

Let's assume we want to create a basic RePast model with the following characteristics:

Agents move around a gridded landscape
Agents always move in a straight line in one of the eight Moore-neighborhood directions
Each cell in the landscape may contain some money; when agents encounter a cell with money they pick it up and carry it with them.
When an agent attempts to move onto a square occupied by another agent, the collision causes the moving agent to give to the agent that was hit one unit of the money it was carrying, and choose a new direction (possibly the same one as before, but no move is permitted in this turn)
Agents have a lifespan of between some minimum and maximum values; when an agent dies, any money it is carrying is spread randomly onto the landscape and the agent is removed. The dead agent is replaced with a newly born agent in a different location with a different lifespan.

To achieve this, we will need three files: the class that instantiates the SimModel object, a class specifying the agents, and a class describing the space. Create these three classes in a new package and name them:

CarryDropModel
CarryDropAgent
CarryDropSpace

Carry Drop Model will include the Main method, which will instantiate the SimModel object in a manner to be discussed. The code for the three files, using the template discussed in the previous section, is initially as follows (note that we keep the 'NumAgents' parameter):

CarryDropModel

// CarryDropModel
package demo;

import uchicago.src.sim.engine.Schedule;
import uchicago.src.sim.engine.SimModelImpl;

public class CarryDropModel extends SimModelImpl {

  private Schedule schedule;
  private int numAgents;

  public String getName(){
    return "Carry And Drop";
  }

  public void setup(){
  }

  public void begin(){
    buildModel();
    buildSchedule();
    buildDisplay();
  }

  public void buildModel(){
  }

  public void buildSchedule(){
  }

  public void buildDisplay(){
  }

  public Schedule getSchedule(){
    return schedule;
  }

  public String[] getInitParam(){
    String[] initParams = { "NumAgents" };
    return initParams;
  }

  public int getNumAgents(){
    return numAgents;
  }

  public void setNumAgents(int na){
    numAgents = na;
  }

  public static void main(String[] args) {
  }

}

CarryDropAgent

// CarryDropAgent
package demo;

public class CarryDropAgent {

}

CarryDropSpace

// CarryDropSpace
package demo;

public class CarryDropSpace {

}

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A RePast Tutorial by John T. Murphy, University of Arizona & Arizona State University (contact)