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#!/usr/bin/python3
# -*- coding: utf-8 -*-
import numpy as np
import torch
import torch.nn as nn
import torch.nn.functional as F
# Transformer (encoder) https://github.com/jadore801120/attention-is-all-you-need-pytorch
# Original Copyright 2017 Victor Huang
# MIT License (https://opensource.org/licenses/MIT)
class ScaledDotProductAttention(nn.Module):
"""
Scaled Dot-Product Attention
"""
def __init__(self, temperature, attn_dropout=0.1):
super().__init__()
self.temperature = temperature
self.dropout = nn.Dropout(attn_dropout)
def forward(self, q, k, v, mask=None):
attn = torch.matmul(q / self.temperature, k.transpose(2, 3))
if mask is not None:
attn = attn.masked_fill(mask == 0, -1e9)
attn = self.dropout(F.softmax(attn, dim=-1))
output = torch.matmul(attn, v)
return output, attn
class MultiHeadAttention(nn.Module):
"""
Multi-Head Attention module
"""
def __init__(self, n_head, d_model, d_k, d_v, dropout=0.1):
super().__init__()
self.n_head = n_head
self.d_k = d_k
self.d_v = d_v
self.w_qs = nn.Linear(d_model, n_head * d_k, bias=False)
self.w_ks = nn.Linear(d_model, n_head * d_k, bias=False)
self.w_vs = nn.Linear(d_model, n_head * d_v, bias=False)
self.fc = nn.Linear(n_head * d_v, d_model, bias=False)
self.attention = ScaledDotProductAttention(temperature=d_k ** 0.5)
self.dropout = nn.Dropout(dropout)
self.layer_norm = nn.LayerNorm(d_model, eps=1e-6)
def forward(self, q, k, v, mask=None):
d_k, d_v, n_head = self.d_k, self.d_v, self.n_head
sz_b, len_q, len_k, len_v = q.size(0), q.size(1), k.size(1), v.size(1)
residual = q
# Pass through the pre-attention projection: b x lq x (n*dv)
# Separate different heads: b x lq x n x dv
q = self.w_qs(q).view(sz_b, len_q, n_head, d_k)
k = self.w_ks(k).view(sz_b, len_k, n_head, d_k)
v = self.w_vs(v).view(sz_b, len_v, n_head, d_v)
# Transpose for attention dot product: b x n x lq x dv
q, k, v = q.transpose(1, 2), k.transpose(1, 2), v.transpose(1, 2)
if mask is not None:
mask = mask.unsqueeze(1) # For head axis broadcasting.
q, attn = self.attention(q, k, v, mask=mask)
# Transpose to move the head dimension back: b x lq x n x dv
# Combine the last two dimensions to concatenate all the heads together: b x lq x (n*dv)
q = q.transpose(1, 2).contiguous().view(sz_b, len_q, -1)
q = self.dropout(self.fc(q))
q += residual
q = self.layer_norm(q)
return q, attn
class PositionwiseFeedForward(nn.Module):
"""
A two-feed-forward-layer module
"""
def __init__(self, d_in, d_hid, dropout=0.1):
super().__init__()
self.w_1 = nn.Linear(d_in, d_hid) # position-wise
self.w_2 = nn.Linear(d_hid, d_in) # position-wise
self.layer_norm = nn.LayerNorm(d_in, eps=1e-6)
self.dropout = nn.Dropout(dropout)
def forward(self, x):
residual = x
x = self.w_2(F.relu(self.w_1(x)))
x = self.dropout(x)
x += residual
x = self.layer_norm(x)
return x
def get_subsequent_mask(seq):
"""
For masking out the subsequent info.
"""
sz_b, len_s = seq.size()
subsequent_mask = (1 - torch.triu(
torch.ones((1, len_s, len_s), device=seq.device), diagonal=1)).bool()
return subsequent_mask
class PositionalEncoding(nn.Module):
def __init__(self, d_hid, n_position=200):
super(PositionalEncoding, self).__init__()
# Not a parameter
self.register_buffer('pos_table', self._get_sinusoid_encoding_table(n_position, d_hid))
def _get_sinusoid_encoding_table(self, n_position, d_hid):
"""
Sinusoid position encoding table
"""
# TODO: make it with torch instead of numpy
def get_position_angle_vec(position):
return [position / np.power(10000, 2 * (hid_j // 2) / d_hid) for hid_j in range(d_hid)]
sinusoid_table = np.array([get_position_angle_vec(pos_i) for pos_i in range(n_position)])
sinusoid_table[:, 0::2] = np.sin(sinusoid_table[:, 0::2]) # dim 2i
sinusoid_table[:, 1::2] = np.cos(sinusoid_table[:, 1::2]) # dim 2i+1
return torch.FloatTensor(sinusoid_table).unsqueeze(0)
def forward(self, x):
return x + self.pos_table[:, :x.size(1)].clone().detach()
class EncoderLayer(nn.Module):
"""
Compose with two layers
"""
def __init__(self, d_model, d_inner, n_head, d_k, d_v, dropout=0.0):
super(EncoderLayer, self).__init__()
self.slf_attn = MultiHeadAttention(n_head, d_model, d_k, d_v, dropout=dropout)
self.pos_ffn = PositionwiseFeedForward(d_model, d_inner, dropout=dropout)
def forward(self, enc_input, slf_attn_mask=None):
enc_output, enc_slf_attn = self.slf_attn(
enc_input, enc_input, enc_input, mask=slf_attn_mask)
enc_output = self.pos_ffn(enc_output)
return enc_output, enc_slf_attn
class TransformerEncoder(nn.Module):
"""
A encoder model with self attention mechanism.
"""
def __init__(
self, d_word_vec=512, n_layers=2, n_head=8, d_k=64, d_v=64,
d_model=512, d_inner=2048, dropout=0.1, n_position=624, scale_emb=False):
super().__init__()
# self.src_word_emb = nn.Embedding(n_src_vocab, d_word_vec, padding_idx=pad_idx)
if n_position > 0:
self.position_enc = PositionalEncoding(d_word_vec, n_position=n_position)
else:
self.position_enc = lambda x: x
self.dropout = nn.Dropout(p=dropout)
self.layer_stack = nn.ModuleList([
EncoderLayer(d_model, d_inner, n_head, d_k, d_v, dropout=dropout)
for _ in range(n_layers)])
self.layer_norm = nn.LayerNorm(d_model, eps=1e-6)
self.scale_emb = scale_emb
self.d_model = d_model
def forward(self, src_seq, src_mask, return_attns=False):
enc_slf_attn_list = []
# -- Forward
# enc_output = self.src_word_emb(src_seq)
enc_output = src_seq
if self.scale_emb:
enc_output *= self.d_model ** 0.5
enc_output = self.dropout(self.position_enc(enc_output))
enc_output = self.layer_norm(enc_output)
for enc_layer in self.layer_stack:
enc_output, enc_slf_attn = enc_layer(enc_output, slf_attn_mask=src_mask)
enc_slf_attn_list += [enc_slf_attn] if return_attns else []
if return_attns:
return enc_output, enc_slf_attn_list
return enc_output
if __name__ == '__main__':
pass
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