fix: boltzmann wealth model network (#270)

Author: jchanke

examples/boltzmann_wealth_model_network/README.md

@@ -10,31 +10,29 @@ In this network implementation, agents must be located on a node, with a limit o
 
 As the model runs, the distribution of wealth among agents goes from being perfectly uniform (all agents have the same starting wealth), to highly skewed -- a small number have high wealth, more have none at all.
 
-JavaScript library used in this example to render the network: [sigma.js](http://sigmajs.org/).
-
 ## Installation
 
-To install the dependencies use pip and the requirements.txt in this directory. e.g.
+To install the dependencies use `pip` to install `mesa[rec]`
 
-```
-    $ pip install -r requirements.txt
+```bash
+    $ pip install mesa[rec]
 ```
 
 ## How to Run
 
-To run the model interactively, run ``mesa runserver`` in this directory. e.g.
+To run the model interactively, run ``solara run`` in this directory. e.g.
 
-```
-    $ mesa runserver
+```bash
+    $ solara run app.py
 ```
 
-Then open your browser to [http://127.0.0.1:8521/](http://127.0.0.1:8521/) and press Reset, then Run.
+Then open your browser to [http://localhost:8765/](http://localhost:8765/) and press Reset, then Run.
 
 ## Files
 
-* ``run.py``: Launches a model visualization server.
-* ``model.py``: Contains the agent class, and the overall model class.
-* ``server.py``: Defines classes for visualizing the model (network layout) in the browser via Mesa's modular server, and instantiates a visualization server.
+* ``model.py``: Contains creation of agents, the network, and management of agent execution.
+* ``agents.py``: Contains logic for giving money, and moving on the network.
+* ``app.py``: Contains the code for the interactive Solara visualization.
 
 ## Further Reading
 

examples/boltzmann_wealth_model_network/app.py

@@ -0,0 +1,96 @@
+from boltzmann_wealth_model_network.model import BoltzmannWealthModelNetwork
+from mesa.mesa_logging import INFO, log_to_stderr
+from mesa.visualization import (
+    SolaraViz,
+    make_plot_component,
+    make_space_component,
+)
+
+log_to_stderr(INFO)
+
+
+# Tells Solara how to draw each agent.
+def agent_portrayal(agent):
+    return {
+        "color": agent.wealth,  # using a colormap to convert wealth to color
+        "size": 50,
+    }
+
+
+model_params = {
+    "seed": {
+        "type": "InputText",
+        "value": 42,
+        "label": "Random seed",
+    },
+    "n": {
+        "type": "SliderInt",
+        "value": 7,
+        "label": "Number of agents",
+        "min": 2,
+        "max": 10,
+        "step": 1,
+        # "description": "Choose how many agents to include in the model",
+    },
+    "num_nodes": {
+        "type": "SliderInt",
+        "value": 10,
+        "label": "Number of nodes",
+        "min": 3,
+        "max": 12,
+        "step": 1,
+        # "description": "Choose how many nodes to include in the model, with at least the same number of agents",
+    },
+}
+
+
+def post_process(ax):
+    ax.get_figure().colorbar(ax.collections[0], label="wealth", ax=ax)
+
+
+# Create initial model instance
+money_model = BoltzmannWealthModelNetwork(n=7, num_nodes=10, seed=42)
+
+# Create visualization elements. The visualization elements are Solara
+# components that receive the model instance as a "prop" and display it in a
+# certain way. Under the hood these are just classes that receive the model
+# instance. You can also author your own visualization elements, which can also
+# be functions that receive the model instance and return a valid Solara
+# component.
+
+SpaceGraph = make_space_component(
+    agent_portrayal, cmap="viridis", vmin=0, vmax=10, post_process=post_process
+)
+GiniPlot = make_plot_component("Gini")
+
+# Create the SolaraViz page. This will automatically create a server and display
+# the visualization elements in a web browser.
+#
+# Display it using the following command in the example directory:
+#   solara run app.py
+# It will automatically update and display any changes made to this file.
+
+page = SolaraViz(
+    money_model,
+    components=[SpaceGraph, GiniPlot],
+    model_params=model_params,
+    name="Boltzmann Wealth Model: Network",
+)
+page  # noqa
+
+
+# In a notebook environment, we can also display the visualization elements
+# directly.
+#
+#   SpaceGraph(model1)
+#   GiniPlot(model1)
+
+# The plots will be static. If you want to pick up model steps,
+# you have to make the model reactive first
+#
+#   reactive_model = solara.reactive(model1)
+#   SpaceGraph(reactive_model)
+
+# In a different notebook block:
+#
+#   reactive_model.value.step()

examples/boltzmann_wealth_model_network/boltzmann_wealth_model_network/agents.py

@@ -0,0 +1,36 @@
+from mesa.discrete_space import CellAgent
+
+
+class MoneyAgent(CellAgent):
+    """An agent with fixed initial wealth.
+
+    Each agent starts with 1 unit of wealth and can give 1 unit to other agents
+    if they occupy the same cell.
+
+    Attributes:
+        wealth (int): The agent's current wealth (starts at 1)
+    """
+
+    def __init__(self, model):
+        """Create a new agent.
+
+        Args:
+            model (Model): The model instance that contains the agent
+        """
+        super().__init__(model)
+        self.wealth = 1
+
+    def give_money(self):
+        neighbors = [agent for agent in self.cell.neighborhood.agents if agent != self]
+        if len(neighbors) > 0:
+            other = self.random.choice(neighbors)
+            other.wealth += 1
+            self.wealth -= 1
+
+    def step(self):
+        empty_neighbors = [cell for cell in self.cell.neighborhood if cell.is_empty]
+        if empty_neighbors:
+            self.cell = self.random.choice(empty_neighbors)
+
+        if self.wealth > 0:
+            self.give_money()

examples/boltzmann_wealth_model_network/boltzmann_wealth_model_network/model.py

@@ -1,72 +1,45 @@
-import mesa
 import networkx as nx
+from mesa import Model
+from mesa.datacollection import DataCollector
+from mesa.discrete_space import Network
 
+from .agents import MoneyAgent
 
-def compute_gini(model):
-    agent_wealths = [agent.wealth for agent in model.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 BoltzmannWealthModelNetwork(mesa.Model):
+class BoltzmannWealthModelNetwork(Model):
     """A model with some number of agents."""
 
-    def __init__(self, num_agents=7, num_nodes=10):
-        super().__init__()
-        self.num_agents = num_agents
+    def __init__(self, n=7, num_nodes=10, seed=None):
+        super().__init__(seed=seed)
+
+        self.num_agents = n
         self.num_nodes = num_nodes if num_nodes >= self.num_agents else self.num_agents
         self.G = nx.erdos_renyi_graph(n=self.num_nodes, p=0.5)
-        self.grid = mesa.experimental.cell_space.Network(
-            self.G, random=self.random, capacity=1
-        )
+        self.grid = Network(self.G, capacity=1, random=self.random)
 
-        self.datacollector = mesa.DataCollector(
-            model_reporters={"Gini": compute_gini},
-            agent_reporters={"Wealth": lambda _: _.wealth},
+        # Set up data collection
+        self.datacollector = DataCollector(
+            model_reporters={"Gini": self.compute_gini},
+            agent_reporters={"Wealth": "wealth"},
         )
 
+        # Create agents; add the agent to a random node
+        # TODO: change to MoneyAgent.create_agents(...)
         list_of_random_nodes = self.random.sample(list(self.G), self.num_agents)
-
-        # Create agents
         for position in list_of_random_nodes:
             agent = MoneyAgent(self)
-
-            # Add the agent to a random node
             agent.move_to(self.grid[position])
 
         self.running = True
         self.datacollector.collect(self)
 
     def step(self):
-        self.agents.shuffle_do("step")
-        # collect data
-        self.datacollector.collect(self)
-
-    def run_model(self, n):
-        for i in range(n):
-            self.step()
-
-
-class MoneyAgent(mesa.experimental.cell_space.CellAgent):
-    """An agent with fixed initial wealth."""
-
-    def __init__(self, model):
-        super().__init__(model)
-        self.wealth = 1
-
-    def give_money(self):
-        neighbors = [agent for agent in self.cell.neighborhood.agents if not self]
-        if len(neighbors) > 0:
-            other = self.random.choice(neighbors)
-            other.wealth += 1
-            self.wealth -= 1
-
-    def step(self):
-        empty_neighbors = [cell for cell in self.cell.neighborhood if cell.is_empty]
-        if empty_neighbors:
-            self.cell = self.random.choice(empty_neighbors)
-
-        if self.wealth > 0:
-            self.give_money()
+        self.agents.shuffle_do("step")  # Activate all agents in random order
+        self.datacollector.collect(self)  # collect data
+
+    def compute_gini(self):
+        agent_wealths = [agent.wealth for agent in self.agents]
+        x = sorted(agent_wealths)
+        N = self.num_agents
+        B = sum(xi * (N - i) for i, xi in enumerate(x)) / (N * sum(x))
+        return 1 + (1 / N) - 2 * B