Added federated learning

machine_learning/federated_learning/__init__.py

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+# Package for machine_learning.federated_learning
+__all__ = ["federated_averaging"]

machine_learning/federated_learning/federated_averaging.py

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+"""
+Federated Learning: enables machine learning on distributed data by moving the training to the data, instead of moving the data to the training.
+Here’s a one-liner explanation:
+ -Centralized machine learning: move the data to the computation.
+ -Federated (machine) Learning: move the computation to the data.
+
+This script demonstrates the working of the Federated Averaging algorithm (FedAvg)
+using a minimal, from-scratch approach with only NumPy.
+
+Overview:
+- Synthetic data is generated and distributed among several clients.
+- Each client performs local gradient-based updates on its dataset.
+- The central server combines all updated client models by averaging them
+  according to the number of samples each client has.
+- The process repeats for multiple communication rounds.
+
+Key Functions:
+    ▪ create_client_datasets(...)
+    ▪ initialize_parameters(...)
+    ▪ client_update(...)
+    ▪ aggregate_models(...)
+    ▪ evaluate_global_model(...)
+    ▪ run_federated_training(...)
+
+Example Usage:
+   we can use in python federated_learning_simulation.py
+
+Reference :
+
+-(GitHub): "Federated Learning from Scratch (NumPy-based)"
+  Ex: https://github.com/omar-fl/federated-learning-from-scratch
+-(Medium article): “Federated Learning from Scratch with NumPy”
+  Ex: https://medium.com/@niveditapatnaik/federated-learning-from-scratch-with-numpy-ff9c62a2a4a9
+"""
+
+from typing import List, Tuple
+import numpy as np
+
+
+def create_client_datasets(
+    n_clients: int,
+    samples_each: int,
+    n_features: int,
+    noise: float = 0.1,
+    seed: int = 42
+) -> List[Tuple[np.ndarray, np.ndarray]]:
+    """
+    Generates synthetic linear regression datasets for multiple clients.
+    Each dataset includes a bias term and Gaussian noise.
+
+    Returns:
+        A list containing tuples of (X, y) for each client.
+        X has shape (samples_each, n_features + 1).
+    """
+    rng = np.random.default_rng(seed)
+    true_weights = rng.normal(0, 1, n_features + 1)
+    clients = []
+
+    for _ in range(n_clients):
+        X = rng.normal(0, 1, (samples_each, n_features))
+        X_bias = np.c_[np.ones((samples_each, 1)), X]
+        y = X_bias @ true_weights + rng.normal(0, noise, samples_each)
+        clients.append((X_bias, y))
+
+    return clients
+
+
+def initialize_parameters(n_params: int, seed: int = 0) -> np.ndarray:
+    """
+    Initialize model parameters (weights + bias) randomly.
+
+    >>> params = initialize_parameters(3, seed=0)
+    >>> len(params)
+    3
+    >>> isinstance(params, np.ndarray)
+    True
+    """
+    rng = np.random.default_rng(seed)
+    return rng.normal(0, 0.01, n_params)
+
+
+def mean_squared_error(params: np.ndarray, X: np.ndarray, y: np.ndarray) -> float:
+    """Computes mean squared error for predictions on dataset (X, y).
+         >>> params = np.array([0.0, 1.0])
+         >>> X = np.array([[1.0, 0.0], [1.0, 1.0]])
+         >>> y = np.array([0.0, 2.0])
+         >>> mean_squared_error(params, X, y)
+         0.5
+    """
+    predictions = X @ params
+    return float(np.mean((predictions - y) ** 2))
+
+
+def evaluate_global_model(params: np.ndarray, client_data: List[Tuple[np.ndarray, np.ndarray]]) -> float:
+    """Evaluates the average global MSE across all client datasets."""
+    total_loss, total_samples = 0.0, 0
+
+    for X, y in client_data:
+        total_loss += np.sum((X @ params - y) ** 2)
+        total_samples += len(y)
+
+    return float(total_loss / total_samples)
+
+
+def client_update(
+    params: np.ndarray,
+    X: np.ndarray,
+    y: np.ndarray,
+    lr: float = 0.01,
+    epochs: int = 1,
+    batch_size: int = 0
+) -> np.ndarray:
+    """
+    Performs local training on a client's dataset.
+    Uses basic gradient descent (full batch or mini-batch depending on batch_size).
+    """
+    updated_params = params.copy()
+    n_samples = len(y)
+
+    for _ in range(epochs):
+        if batch_size <= 0 or batch_size >= n_samples:
+            # Full-batch gradient descent
+            preds = X @ updated_params
+            grad = (2 / n_samples) * (X.T @ (preds - y))
+            updated_params -= lr * grad
+        else:
+            # Mini-batch gradient descent
+            order = np.random.permutation(n_samples)
+            for i in range(0, n_samples, batch_size):
+                idx = order[i:i + batch_size]
+                Xb, yb = X[idx], y[idx]
+                preds = Xb @ updated_params
+                grad = (2 / len(yb)) * (Xb.T @ (preds - yb))
+                updated_params -= lr * grad
+
+    return updated_params
+
+
+def aggregate_models(models: List[np.ndarray], sizes: List[int]) -> np.ndarray:
+    """
+    Combines client models by computing a weighted average
+    based on the number of samples each client used.
+
+      >>> w1 = np.array([1.0, 2.0])
+      >>> w2 = np.array([3.0, 4.0])
+      >>> aggregate_models([w1, w2], [1, 1])
+    array([2., 3.])
+    """
+    total_samples = sum(sizes)
+    if total_samples == 0:
+        raise ValueError("Cannot aggregate: total sample size is zero.")
+
+    aggregated = np.zeros_like(models[0], dtype=float)
+    for w, n in zip(models, sizes):
+        aggregated += (n / total_samples) * w
+    return aggregated
+
+
+def run_federated_training(
+    clients: List[Tuple[np.ndarray, np.ndarray]],
+    rounds: int = 10,
+    local_epochs: int = 1,
+    lr: float = 0.01,
+    batch_size: int = 0,
+    seed: int = 0
+) -> Tuple[np.ndarray, List[float]]:
+    """
+    Runs the full FedAvg simulation for the given client datasets.
+
+    Returns:
+        final_parameters : np.ndarray
+        loss_history : list of MSE values over communication rounds
+    """
+    n_params = clients[0][0].shape[1]
+    global_params = initialize_parameters(n_params, seed)
+    history = []
+
+    for round_num in range(1, rounds + 1):
+        client_models, client_sizes = [], []
+
+        for X, y in clients:
+            local_params = client_update(global_params, X, y, lr, local_epochs, batch_size)
+            client_models.append(local_params)
+            client_sizes.append(len(y))
+
+        global_params = aggregate_models(client_models, client_sizes)
+        mse = evaluate_global_model(global_params, clients)
+        history.append(mse)
+
+        print(f"Round {round_num}/{rounds} - Global MSE: {mse:.6f}")
+
+    return global_params, history
+
+
+if __name__ == "__main__":
+    # Example demonstration
+    datasets = create_client_datasets(n_clients=5, samples_each=200, n_features=3, noise=0.5, seed=123)
+    final_model, loss_curve = run_federated_training(datasets, rounds=12, local_epochs=2, lr=0.05)
+
+    print("\nFinal model parameters:\n", np.round(final_model, 4))
+
+    try:
+        import matplotlib.pyplot as plt
+        plt.plot(loss_curve, marker='o')
+        plt.title("Federated Averaging - Training Loss Curve")
+        plt.xlabel("Round")
+        plt.ylabel("Mean Squared Error")
+        plt.grid(True)
+        plt.show()
+    except ImportError:
+        pass
+
+"""
+ for testing:
+    Create "tests/test_federated_averaging.py"
+
+    " import numpy as np
+      from machine_learning.federated_learning import federated_averaging as fed
+
+      def test_loss_reduction_in_fedavg():
+      # Define a small, reproducible test scenario
+      clients = fed.create_synthetic_clients(
+        n_clients=3,
+        samples_per_client=80,
+        n_features=2,
+        noise_level=0.3,
+        seed=0
+      ) "
+
+"""