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Dropout

As explained in Math and Architectures of Deep Learning

A regularization method that randomly turns off units during training to reduce co-adaptation and improve generalization.

Dropout is a regularization method for overfitting neural networks. During training, it randomly sets selected perceptron outputs to zero, preventing the network from depending too heavily on a small group of units. section 9.0 section 9.3.6

For unit i in layer l, let δᵢ be a binary mask: δᵢ = 1 with probability pᵢ and δᵢ = 0 with probability 1 − pᵢ. The masked activation is therefore δᵢaᵢ. Dropout is enabled during training and disabled during inference. section 9.3.6

The mask discourages co-adaptation, where correlated units repeatedly produce similar outputs. Because any unit may disappear in a training iteration, learning spreads across multiple units, producing behavior analogous to L2 regularization. section 9.3.6

A three-node layer as an ensemble

A three-node layer has 2³ = 8 possible on/off configurations. Each configuration acts as a subnetwork, with its probability determined by the individual keep probabilities; for example, all three units being active has probability p₀p₁p₂. section 9.3.6

How Math and Architectures of Deep Learning covers it

How deep it goes
Develops the definition, Bernoulli-mask formulation, co-adaptation rationale, subnetwork interpretation, and PyTorch implementation.
Examples
Uses an eight-subnetwork three-node example and a PyTorch sequential model containing two dropout layers.
What you can do after
Apply dropout via PyTorch by inserting torch.nn.Dropout layers into a neural-network architecture.
How it connects
Connects dropout to overfitting, regularization, L2 regularization, co-adaptation, and ensemble-like subnetworks.

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This explainer was generated by Manning's knowledge graph from the text of Math and Architectures of Deep Learning. The section links point to the parts of the book it draws on.