# `Edifice.Blocks.FFN`
[🔗](https://github.com/blasphemetheus/edifice/blob/main/lib/edifice/blocks/ffn.ex#L1)

Feed-Forward Network building blocks for transformer architectures.

Provides standard and gated FFN variants used in the feed-forward sublayer
of transformer blocks. This module unifies the duplicated `build_ffn/3`
pattern found across attention architectures.

## Variants

- **Standard**: `dense(hidden * expansion) -> activation -> dropout -> dense(hidden)`
- **Gated**: Delegates to `SwiGLU.layer/2` for gated linear unit variants

## Usage

    # Standard FFN (default in most transformers)
    ffn = FFN.layer(input, hidden_size: 256)

    # With custom expansion factor and activation
    ffn = FFN.layer(input, hidden_size: 256, expansion_factor: 8, activation: :relu)

    # Gated variant (SwiGLU/GeGLU/ReGLU)
    ffn = FFN.gated_layer(input, hidden_size: 256, activation: :silu)

## References
- "Attention Is All You Need" (Vaswani et al., 2017) - original FFN
- "GLU Variants Improve Transformer" (Shazeer, 2020) - gated variants

# `gated_layer`

```elixir
@spec gated_layer(
  Axon.t(),
  keyword()
) :: Axon.t()
```

Build a gated feed-forward network (SwiGLU/GeGLU/ReGLU).

Delegates to `Edifice.Blocks.SwiGLU.layer/2` with a unified API.

## Options
  - `:hidden_size` - Input/output dimension (required)
  - `:inner_size` - Intermediate dimension (default: hidden_size * 2.667)
  - `:activation` - Gate activation: :silu, :gelu, :relu (default: :silu)
  - `:dropout` - Dropout rate (default: 0.0)
  - `:name` - Layer name prefix (default: "gated_ffn")

# `layer`

```elixir
@spec layer(
  Axon.t(),
  keyword()
) :: Axon.t()
```

Build a standard feed-forward network as an Axon layer.

## Options
  - `:hidden_size` - Input/output dimension (required)
  - `:expansion_factor` - Inner dimension multiplier (default: 4)
  - `:inner_size` - Explicit inner dimension (overrides expansion_factor)
  - `:activation` - Activation function (default: :gelu)
  - `:dropout` - Dropout rate (default: 0.0)
  - `:name` - Layer name prefix (default: "ffn")

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*Consult [api-reference.md](api-reference.md) for complete listing*