added rnn code

Author: shreyakash24

neural_network/recurrent_neural_network.py

@@ -0,0 +1,95 @@
+"""
+Minimal Recurrent Neural Network (RNN) demonstration.
+
+Forward propagation explanation:
+https://towardsdatascience.com/forward-propagation-in-neural-networks-simplified-math-and-code-version-bbcfef6f9250
+RNN fundamentals:
+https://towardsdatascience.com/recurrent-neural-networks-d4642c9bc7ce/
+"""
+
+import math
+import random
+
+
+# Sigmoid activation
+def sigmoid_function(value: float, deriv: bool = False) -> float:
+    """Return the sigmoid function of a float.
+
+    >>> round(sigmoid_function(3.5), 4)
+    0.9707
+    >>> round(sigmoid_function(0.5, True), 4)
+    0.25
+    """
+    if deriv:
+        return value * (1 - value)
+    return 1 / (1 + math.exp(-value))
+
+
+# Initial constants
+INITIAL_VALUE = 0.02  # learning rate
+SEQUENCE_LENGTH = 5   # time steps in the sequence
+
+
+def forward_propagation_rnn(expected: int, number_propagations: int) -> float:
+    """Return the value found after RNN forward propagation training.
+
+    >>> res = forward_propagation_rnn(50, 500_000)
+    >>> res > 45 and res < 55
+    True
+
+    >>> res = forward_propagation_rnn(50, 500)
+    >>> res > 48 and res < 50
+    True
+    """
+    random.seed(0)
+
+    # Random weight initialization
+    W_xh = (random.random() * 2 - 1)  # Input to hidden
+    W_hh = (random.random() * 2 - 1)  # Hidden to hidden (recurrent)
+    W_hy = (random.random() * 2 - 1)  # Hidden to output
+
+    # Training loop
+    for _ in range(number_propagations):
+        h_prev = 0.0  # hidden state starts at zero
+        total_error = 0.0
+
+        # Forward pass through time
+        for t in range(SEQUENCE_LENGTH):
+            # Fake input sequence: small constant or could be pattern-based
+            x_t = INITIAL_VALUE
+
+            # Hidden state update
+            h_t = sigmoid_function(W_xh * x_t + W_hh * h_prev)
+
+            # Output
+            y_t = sigmoid_function(W_hy * h_t)
+
+            # Error (target distributed over time steps)
+            error_t = (expected / 100) - y_t
+            total_error += abs(error_t)
+
+            # Backpropagation Through Time (simplified)
+            d_y = error_t * sigmoid_function(y_t, True)
+            d_h = d_y * W_hy * sigmoid_function(h_t, True)
+
+            # Weight updates
+            W_hy += INITIAL_VALUE * d_y * h_t
+            W_xh += INITIAL_VALUE * d_h * x_t
+            W_hh += INITIAL_VALUE * d_h * h_prev
+
+            # Move to next time step
+            h_prev = h_t
+
+    # Final output after training
+    final_output = y_t * 100
+    return final_output
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()
+
+    expected = int(input("Expected value: "))
+    number_propagations = int(input("Number of propagations: "))
+    print(forward_propagation_rnn(expected, number_propagations))