FLASH pytorch

FLASH-Pytorch

线性时间内变压器质量论文中提出的变压器变体的实现

安装

$ pip install FLASH-pytorch

用法

本文的主要新颖电路是“门控注意力单元”，他们声称它可以取代多头注意力，同时将其减少到只有一个头。

它使用 relu 平方激活代替了 softmax，其激活首次出现在 Primer 论文中，并且在 ReLA Transformer 中使用了 ReLU。门控风格似乎主要受到 gMLP 的启发。

 import torch
from flash_pytorch import GAU

gau = GAU (
    dim = 512 ,
    query_key_dim = 128 ,     # query / key dimension
    causal = True ,           # autoregressive or not
    expansion_factor = 2 ,    # hidden dimension = dim * expansion_factor
    laplace_attn_fn = True   # new Mega paper claims this is more stable than relu squared as attention function
)

x = torch . randn ( 1 , 1024 , 512 )
out = gau ( x ) # (1, 1024, 512)

然后，作者将GAU与 Katharopoulos 线性注意力相结合，使用序列分组来克服自回归线性注意力的已知问题。

这种二次门控注意力单元与分组线性注意力的组合被他们命名为 FLASH

你也可以很容易地使用它

 import torch
from flash_pytorch import FLASH

flash = FLASH (
    dim = 512 ,
    group_size = 256 ,             # group size
    causal = True ,                # autoregressive or not
    query_key_dim = 128 ,          # query / key dimension
    expansion_factor = 2. ,        # hidden dimension = dim * expansion_factor
    laplace_attn_fn = True   # new Mega paper claims this is more stable than relu squared as attention function
)

x = torch . randn ( 1 , 1111 , 512 )     # sequence will be auto-padded to nearest group size
out = flash ( x ) # (1, 1111, 512)

最后，您可以使用本文中提到的完整 FLASH 变压器。这包含论文中提到的所有位置嵌入。绝对位置嵌入使用缩放正弦曲线。 GAU 二次注意力会得到单向 T5 相对位置偏差。最重要的是，GAU 注意力和线性注意力都将被旋转嵌入（RoPE）。

 import torch
from flash_pytorch import FLASHTransformer

model = FLASHTransformer (
    num_tokens = 20000 ,          # number of tokens
    dim = 512 ,                   # model dimension
    depth = 12 ,                  # depth
    causal = True ,               # autoregressive or not
    group_size = 256 ,            # size of the groups
    query_key_dim = 128 ,         # dimension of queries / keys
    expansion_factor = 2. ,       # hidden dimension = dim * expansion_factor
    norm_type = 'scalenorm' ,     # in the paper, they claimed scalenorm led to faster training at no performance hit. the other option is 'layernorm' (also default)
    shift_tokens = True          # discovered by an independent researcher in Shenzhen @BlinkDL, this simply shifts half of the feature space forward one step along the sequence dimension - greatly improved convergence even more in my local experiments
)

x = torch . randint ( 0 , 20000 , ( 1 , 1024 ))
logits = model ( x ) # (1, 1024, 20000) 

自回归 Enwik8 测试

$ python train.py

引文

 @article { Hua2022TransformerQI ,
    title   = { Transformer Quality in Linear Time } ,
    author  = { Weizhe Hua and Zihang Dai and Hanxiao Liu and Quoc V. Le } ,
    journal = { ArXiv } ,
    year    = { 2022 } ,
    volume  = { abs/2202.10447 }
}

 @software { peng_bo_2021_5196578 ,
    author    = { PENG Bo } ,
    title     = { BlinkDL/RWKV-LM: 0.01 } ,
    month     = { aug } ,
    year      = { 2021 } ,
    publisher = { Zenodo } ,
    version   = { 0.01 } ,
    doi       = { 10.5281/zenodo.5196578 } ,
    url       = { https://doi.org/10.5281/zenodo.5196578 }
}

 @inproceedings { Ma2022MegaMA ,
    title   = { Mega: Moving Average Equipped Gated Attention } ,
    author  = { Xuezhe Ma and Chunting Zhou and Xiang Kong and Junxian He and Liangke Gui and Graham Neubig and Jonathan May and Luke Zettlemoyer } ,
    year    = { 2022 }
}