nn.py

import numpy as np


class NeuralNetwork:

    def __init__(self, layer_sizes):
        """
        Neural Network initialization.
        Given layer_sizes as an input, you have to design a Fully Connected Neural Network architecture here.
        :param layer_sizes: A list containing neuron numbers in each layers. For example [3, 10, 2] means that there are
        3 neurons in the input layer, 10 neurons in the hidden layer, and 2 neurons in the output layer.
        """
        # TODO (Implement FCNNs architecture here)
        self.in_size = layer_sizes[0]
        self.w1 = np.random.standard_normal((layer_sizes[1], layer_sizes[0]))
        self.w2 = np.random.standard_normal((layer_sizes[2], layer_sizes[1]))
        self.b1 = np.zeros((layer_sizes[1], 1))
        self.b2 = np.zeros((layer_sizes[2], 1))

    def activation(self, x):
        """
        The activation function of our neural network, e.g., Sigmoid, ReLU.
        :param x: Vector of a layer in our network.
        :return: Vector after applying activation function.
        """
        # TODO (Implement activation function here)
        # sigmoid
        s = 1 / (1 + np.exp(-x))
        # r = np.maximum(x, 0)
        return s

    def forward(self, x):
        """
        Receives input vector as a parameter and calculates the output vector based on weights and biases.
        :param x: Input vector which is a numpy array.
        :return: Output vector
        """
        # TODO (Implement forward function here)
        x = x.reshape((self.in_size, 1))
        z1 = self.w1 @ x + self.b1
        a1 = self.activation(z1)
        z2 = self.w2 @ a1 + self.b2
        a2 = self.activation(z2)
        return a2