Deep learning algorithms process data through layered artificial neural networks designed to automatically learn patterns from raw inputs. These networks consist of interconnected nodes (neurons) organized into input, hidden, and output layers. Each layer transforms data using weights and activation functions, gradually extracting higher-level features. For example, in image recognition, early layers might detect edges or textures, while deeper layers identify complex shapes or objects. The term “deep” refers to the multiple layers that enable hierarchical feature learning, distinguishing it from simpler neural networks with few hidden layers.
Training deep learning models involves two key steps: forward propagation and backpropagation. During forward propagation, input data passes through the network, generating predictions. A loss function then measures the difference between predictions and actual targets (e.g., classification labels). Backpropagation calculates gradients of this loss with respect to the model’s weights using the chain rule from calculus. Optimizers like stochastic gradient descent (SGD) adjust the weights to minimize the loss iteratively. For instance, when training a model to recognize handwritten digits (MNIST dataset), the network might start with random weights, produce garbled predictions, and gradually refine its parameters over thousands of labeled examples until accuracy improves.
Practical implementation relies on frameworks like TensorFlow or PyTorch, which handle automatic differentiation and GPU acceleration. Common architectures include convolutional neural networks (CNNs) for grid-like data (images) and transformers for sequential data (text). Challenges include avoiding overfitting—addressed through techniques like dropout or data augmentation—and selecting appropriate hyperparameters (e.g., learning rate, batch size). For example, a CNN trained on medical images might use convolutional layers to capture spatial patterns, max-pooling layers to reduce dimensionality, and fully connected layers for final classification. Developers often start with pre-trained models (e.g., ResNet) and fine-tune them for specific tasks, balancing computational resources and model complexity.