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Hydra

Hydra: Bidirectional State Space Models Through Generalized Matrix Mixers
Sukjun Hwang*, Aakash Lahoti*, Tri Dao, Albert Gu
Paper: https://arxiv.org/abs/2407.09941
Blogpost: https://goombalab.github.io/blog/2024/hydra-part1-matrix-mixer/

About

Installation

Follow the installation section of Mamba; simply,

pip install mamba-ssm

[Option] For training BERT (./hydra/bert), install additional required packages via pip install -r requirements.txt

Usage

Hydra Block

The quasiseparable matrix mixer, Hydra, is our best model for bidirectional sequence processing (details in Section 3).
The implementation is at ./hydra/modules/hydra.py.

import torch
from .hydra import Hydra

batch, length, dim = 2, 64, 16
x = torch.randn(batch, length, dim).to("cuda")
model = Hydra(
    d_model=dim, # Model dimension d_model
    d_state=64,  # SSM state expansion factor
    d_conv=7,    # Local non-causal convolution width
    expand=2,    # Block expansion factor
    use_mem_eff_path=False,    # Nightly release. Thanks to Alston Lo
).to("cuda")
y = model(x)
assert y.shape == x.shape

Matrix Mixer Block

The matrix mixer framework is implemented at ./hydra/modules/matrix_mixer.py.
You can easily integrate your own mixer matrix by following our implementations of various sequence mixers located at ./hydra/modules/matrix_mixers/!

from .hydra import MatrixMixer

model = MatrixMixer(
    """
    matrix_mixer_type: options for matrix_mixer_type
        {'dense', 'toeplitz', 'vandermonde', 'cauchy', 'low_rank', 'attention', 'quasiseparable'}
    is_data_dependent: boolean flag to parameterize the mixer matrix to SAM
    """
    matrix_mixer_type=matrix_mixer_type,
    is_data_dependent=is_data_dependent,
    d_model=dim,    # Model dimension d_model
    qk_dim=qk_dim,  # dimension for QK
).to("cuda")
y = model(x)
assert y.shape == x.shape

BERT

Our code for training BERT (./hydra/bert/) is based on MosaicBERT and M2.

Follow the instructions of MosaicBERT (./hydra/bert/README.md) for details (e.g., setting up dataset and running code).
The default configurations for Hydra and MatrixMixer are located at:

• Pretrain: ./hydra/bert/yamls/pretrain
• Finetune: ./hydra/bert/yamls/finetune

Example commands:

Pretrain Hydra on C4 using a single GPU:

python main.py yamls/pretrain/hydra.yaml

Pretrain Hydra on C4 using 8 GPUs:

composer -n 8 main.py yamls/pretrain/hydra.yaml

Finetune Hydra on GLUE:

python glue.py yamls/finetune/hydra.yaml

Pretrained Weights

Weights of Hydra with 23layers pretrained on C4 are uploaded to HuggingFace.

Acknowledgement

We thank the authors of Mamba, MosaicBERT, and M2 for their wonderful codebases.

Citation

If you use this codebase, or otherwise find our work valuable, please cite Hydra:

@article{hydra,
  title={Hydra: Bidirectional State Space Models Through Generalized Matrix Mixers},
  author={Hwang, Sukjun and Lahoti, Aakash and Dao, Tri and Gu, Albert},
  journal={arXiv preprint arXiv:2407.09941},
  year={2024}
}