MASON (Multi-Agent Simulator Of Neighborhoods… or Networks… or something…) is a fast discrete-event multiagent simulation library core in Java, designed to be the foundation for large custom-purpose Java simulations, and also to provide more than enough functionality for many lightweight simulation needs.

It has an example of Schelling's model in /home/pedro/codigo/mason/sim/app/schelling/Agent.java. The model is composed by reds, blues, empty sites where the players can move, and non-available sites. Following there is an example of calculating the unsatisfaction and moving to another site:

  // get all the places I can go.  This will be slow as we have to rely on grabbing neighbors.
  sch.neighbors.getNeighborsMaxDistance(loc.x,loc.y,sch.neighborhood,false,neighborsX,neighborsY);
    
  // compute value
  double val = 0;
  int threshold = sch.threshold;  // locals a little faster
  int numObjs = neighborsX.numObjs;
  int[] objsX = neighborsX.objs;
  int[] objsY = neighborsY.objs;
  int myVal = locs[x][y];
      
  for(int i=0;i<numObjs;i++)
  {
      if (locs[objsX[i]][objsY[i]] == myVal // just like me
          && !(objsX[i] == x && objsY[i] == y))  // but it's NOT me
      {
          val += 1.0/Math.sqrt((x-objsX[i])*(x-objsX[i]) + (y-objsY[i])*(y-objsY[i]));
          if (val >= threshold) return;  // we're not moving
      }
  }
      
  // find a new spot to live -- a random jump? Move to a nearby location?  Websites differ
  int newLocIndex = state.random.nextInt(sch.emptySpaces.numObjs);
  Int2D newLoc = (Int2D)(sch.emptySpaces.objs[newLocIndex]);
  sch.emptySpaces.objs[newLocIndex] = loc;
      
  // swap colors
  int swap = locs[newLoc.x][newLoc.y];
  locs[newLoc.x][newLoc.y] = locs[loc.x][loc.y];
  locs[loc.x][loc.y] = swap;
  // adopt new position
  loc = newLoc;