initial

.gitignore

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+# Virtualenv
+# http://iamzed.com/2009/05/07/a-primer-on-virtualenv/
+.Python
+[Bb]in
+[Ii]nclude
+[Ll]ib
+[Ll]ib64
+[Ll]ocal
+[Ss]cripts
+pyvenv.cfg
+.venv
+pip-selfcheck.json

ForkliftModel.py

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+import random
+
+from mesa import Agent, Model
+from mesa.time import RandomActivation
+from mesa.space import MultiGrid
+from mesa.datacollection import DataCollector
+
+
+def compute_gini(model):
+    agent_wealths = [agent.wealth for agent in model.schedule.agents]
+    x = sorted(agent_wealths)
+    N = model.num_agents
+    B = sum(xi * (N - i) for i, xi in enumerate(x)) / (N * sum(x))
+    return (1 + (1 / N) - 2 * B)
+
+
+class MoneyModel(Model):
+    """A model with some number of agents."""
+
+    def __init__(self, N, width, height):
+        self.num_agents = N
+        self.running = True
+        self.grid = MultiGrid(height, width, True)
+        self.schedule = RandomActivation(self)
+        self.datacollector = DataCollector(
+            model_reporters={"Gini": compute_gini},
+            agent_reporters={"Wealth": lambda a: a.wealth}
+        )
+        # Create agents
+        for i in range(self.num_agents):
+            a = MoneyAgent(i, self)
+            self.schedule.add(a)
+            # Add the agent to a random grid cell
+            x = random.randrange(self.grid.width)
+            y = random.randrange(self.grid.height)
+            self.grid.place_agent(a, (x, y))
+
+    def step(self):
+        self.datacollector.collect(self)
+        self.schedule.step()
+
+    def run_model(self, n):
+        for i in range(n):
+            self.step()
+
+
+class MoneyAgent(Agent):
+    """ An agent with fixed initial wealth."""
+    def __init__(self, unique_id, model):
+        super().__init__(unique_id, model)
+        self.wealth = 1
+
+    def move(self):
+        possible_steps = self.model.grid.get_neighborhood(
+            self.pos, moore=True, include_center=False
+        )
+        new_position = random.choice(possible_steps)
+        self.model.grid.move_agent(self, new_position)
+
+    def give_money(self):
+        cellmates = self.model.grid.get_cell_list_contents([self.pos])
+        if len(cellmates) > 1:
+            other = random.choice(cellmates)
+            other.wealth += 1
+            self.wealth -= 1
+
+    def step(self):
+        self.move()
+        if self.wealth > 0:
+            self.give_money()