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Depth

As explained in Grokking AI Algorithms, Second Edition

The number of layers is the count of successive computational layers in a neural-network architecture.

Depth is the number of successive computational layers in a neural-network architecture. In an artificial neural network, adding hidden layers lets the model build increasingly high-level abstractions and represent more complex classification boundaries. section 9.13 section 11.11

Depth matters because each layer adds another transformation:

  • Shallow networks can represent simple relationships, such as a fairly simple nonlinear boundary. section 9.13
  • Deeper networks can combine earlier outputs into higher-level abstractions for complex functions across many dimensions. section 9.13
  • Choosing depth usually requires experimentation and iterative improvement rather than a fixed universal value. section 9.13
  • Architecture setup defines the hidden-layer count alongside nodes, activation functions, inputs, outputs, and initial weights. section 9.6

Depth in a toy language model

A Transformer with two layers performs two successive processing steps in its reasoning chain. A larger model with twelve layers can perform a longer sequence of such steps. Depth is only one architectural choice: context window, embedding width, attention heads, and feed-forward size also affect the design. section 11.11

Table 11.7 The hyperparameters for the Transformer framework

Hyperparameter

Rule of thumb

Toy LLM example

Real-world LLM

Vocabulary size (V)

Based on training data

34 sentence pieces

50,000 (more than 250,000 sentence pieces

Context window (T)

Longest prompt you need, rounded to power of 2, that still fits batch on a GPU

32 tokens

1,024 (more than 32,000 tokens)

Width (d)

Start near 4√Vocabulary size

4 channels

768 (more than 20,000 channels)

Depth (L)

1–2 layers per 100,000 characters of training text

2 layers

12 (more than 120 layers

Attention heads (h)

h = Width ÷ 64 (round to even)

1 head

12 (more than 128 heads

Feed-forward size (dn)

dn = 4 × Width is a safe default

Layer 1: 8 neurons

Layer 2: 4 neurons

3,027 (more than 80,000 neurons)

Compare toy and real-world Transformer depths alongside context windows, embedding widths, attention heads, and feed-forward sizes. section 11.11

How Grokking AI Algorithms, Second Edition covers it

How deep it goes
Explains depth through hidden-layer abstractions and Transformer steps, but defers formal optimization or theoretical analysis.
Examples
Uses simple classification boundaries, multilayer ANN architectures, and toy-versus-real-world Transformer configurations.
What you can do after
Evaluate candidate layer counts through architecture design, experimentation, and iterative improvement.
How it connects
Connects depth with hidden layers, activation functions, tensors, Transformers, self-attention, context windows, and embedding width.

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This explainer was generated by Manning's knowledge graph from the text of Grokking AI Algorithms, Second Edition. The section links point to the parts of the book it draws on.