JumpReLU SAE

JumpReLU SAE is a variation of the standard Sparse Autoencoder (SAE) that incorporates the JumpReLU activation function to have an adaptive sparsity without shriking. This involve a learnable thresholding mechanism on each concept. As all SAEs, it include an encoder, a decoder, and a forward method.

• encode returns the pre-codes (z_pre, before ReLU) and codes (z) given an input (x).
• decode returns a reconstructed input (x_hat) based on an input (x).
• forward returns the pre-codes, codes, and reconstructed input.

kernel='silverman', bandwith=1e-3,

The specificity of this architecture is that i contains 2 hyperparamter, a bandwith and a kernel. We strongly encourage you to check the original paper ¹ to know more about JumpReLU.

Basic Usage

from overcomplete import JumpSAE

# define a JumpReLU SAE with input dimension 768 and 10k concepts
sae = JumpSAE(768, 10_000)

# adjust kernel and bandwith
sae = JumpSAE(768, 10_000, bandwith = 1e-2,
              kernel='silverman')

JumpSAE

JumpReLU Sparse Autoencoder (SAE).

__init__(self,
         input_shape,
         nb_concepts,
         kernel='silverman',
         bandwith=0.001,
         encoder_module=None,
         dictionary_params=None,
         device='cpu')

Parameters

• input_shape : int or tuple of int

  • Dimensionality of the input data, do not include batch dimensions.

    It is usually 1d (dim), 2d (seq length, dim) or 3d (dim, height, width).

• nb_concepts : int

  • Number of components/concepts in the dictionary. The dictionary is overcomplete if the number of concepts > in_dimensions.

• kernel : str, optional

  • Kernel function to use in the JumpReLU activation, by default 'silverman'.

    Current options are : - 'rectangle' - 'gaussian' - 'triangular' - 'cosine' - 'epanechnikov' - 'quartic' - 'silverman' - 'cauchy'.

• bandwith : float, optional

  • Bandwith of the kernel, by default 1e-3.

• encoder_module : nn.Module or string, optional

  • Custom encoder module, by default None.

    If None, a simple Linear + BatchNorm default encoder is used.

    If string, the name of the registered encoder module.

• dictionary_params : dict, optional

  • Parameters that will be passed to the dictionary layer.

    See DictionaryLayer for more details.

• device : str, optional

  • Device to run the model on, by default 'cpu'.

forward(self,
        x)

Perform a forward pass through the autoencoder.

Parameters

• x : torch.Tensor

  • Input tensor of shape (batch_size, input_size).

Return

• SAEOuput

  • Return the pre_codes (z_pre), codes (z) and reconstructed input tensor (x_hat).

encode(self,
       x)

Encode input data to latent representation.

Parameters

• x : torch.Tensor

  • Input tensor of shape (batch_size, input_size).

Return

• pre_codes : torch.Tensor

  • Pre-codes tensor of shape (batch_size, nb_components) before the jump operation.

• codes : torch.Tensor

  • Codes, latent representation tensor (z) of shape (batch_size, nb_components).

decode(self,
       z)

Decode latent representation to reconstruct input data.

Parameters

• z : torch.Tensor

  • Latent representation tensor of shape (batch_size, nb_components).

Return

• torch.Tensor

  • Reconstructed input tensor of shape (batch_size, input_size).

get_dictionary(self)

Return the learned dictionary.

Return

• torch.Tensor

  • Learned dictionary tensor of shape (nb_components, input_size).

---

1. Jumping Ahead: Improving Reconstruction Fidelity with JumpReLU Sparse Autoencoders (2024) by Rajamanoharan et al. (2024). ↩