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NNLM的PyTorch实现

A Neural Probabilistic Language Model

 

本文算是训练语言模型的经典之作,Bengio将神经网络引入语言模型的训练中,并得到了词向量这个副产物。词向量对后面深度学习在自然语言处理方面有很大的贡献,也是获取词的语义特征的有效方法

 

其主要架构为三层神经网络,如下图所示

 

 

现在的任务是输入$w_{t-n+1},…,w_{t-1}$这前n-1个单词,然后预测出下一个单词$w_t$

 

数学符号说明:

$C(i)$:单词$w$对应的词向量,其中$i$为词$w$在整个词汇表中的索引
$C$:词向量,大小为$|V|\times m$的矩阵
$|V|$:词汇表的大小,即预料库中去重后的单词个数
$m$:词向量的维度,一般是50到200
$H$:隐藏层的weight
$d$:隐藏层的bias
$U$:输出层的weight
$b$:输出层的bias
$W$:输入层到输出层的weight
$h$:隐藏层神经元个数

计算流程:

 

 

    1. 首先将输入的n-1个单词索引转为词向量,然后将这n-1个词向量进行concat,形成一个(n-1)*w的向量,用X表示

 

    1. 将X送入隐藏层进行计算,$hidden_{out} = tanh(d+X*H)$

 

    1. 输出层共有$|V|$个节点,每个节点$y_i$表示预测下一个单词$i$的概率,$y$的计算公式为$y=b+X*W+hidden_{out}*U$

 

 

代码实现(PyTorch)

 

# code by Tae Hwan Jung @graykode, modify by wmathor
import torch
import torch.nn as nn
import torch.optim as optim
dtype = torch.FloatTensor

 

sentences = [ "i like dog", "i love coffee", "i hate milk"]
word_list = " ".join(sentences).split() # ['i', 'like', 'dog', 'dog', 'i', 'love', 'coffee', 'i', 'hate', 'milk']
word_list = list(set(word_list)) # ['i', 'like', 'dog', 'love', 'coffee', 'hate', 'milk']
word_dict = {w: i for i, w in enumerate(word_list)} # {'i':0, 'like':1, 'dog':2, 'love':3, 'coffee':4, 'hate':5, 'milk':6}
number_dict = {i: w for i, w in enumerate(word_list)} # {0:'i', 1:'like', 2:'dog', 3:'love', 4:'coffee', 5:'hate', 6:'milk'}
n_class = len(word_dict) # number of Vocabulary, just like |V|, in this task n_class=7
# NNLM(Neural Network Language Model) Parameter
n_step = len(sentences[0].split())-1 # n-1 in paper, look back n_step words and predict next word. In this task n_step=2
n_hidden = 2 # h in paper
m = 2 # m in paper, word embedding dim

 

由于PyTorch中输入数据是以mini-batch小批量进行的,下面的函数首先将原始数据(词)全部转为索引,然后通过 TensorDataset()
DataLoader()
编写一个实用的mini-batch迭代器

 

def make_batch(sentences):
    input_batch = []
    target_batch = []
    for sen in sentences:
        word = sen.split()
        input = [word_dict[n] for n in word[:-1]] # [0, 1], [0, 3], [0, 5]
        target = word_dict[word[-1]] # 2, 4, 6
        input_batch.append(input) # [[0, 1], [0, 3], [0, 5]]
        target_batch.append(target) # [2, 4, 6]
    return input_batch, target_batch
input_batch, target_batch = make_batch(sentences)
input_batch = torch.LongTensor(input_batch)
target_batch = torch.LongTensor(target_batch)
dataset = Data.TensorDataset(input_batch, target_batch)
loader = Data.DataLoader(dataset=dataset, batch_size=16, shuffle=True)

 

class NNLM(nn.Module):
  def __init__(self):
    super(NNLM, self).__init__()
    self.C = nn.Embedding(n_class, m)
    self.H = nn.Parameter(torch.randn(n_step * m, n_hidden).type(dtype))
    self.W = nn.Parameter(torch.randn(n_step * m, n_class).type(dtype))
    self.d = nn.Parameter(torch.randn(n_hidden).type(dtype))
    self.U = nn.Parameter(torch.randn(n_hidden, n_class).type(dtype))
    self.b = nn.Parameter(torch.randn(n_class).type(dtype))
  def forward(self, X):
    '''
    X: [batch_size, n_step]
    '''
    X = self.C(X) # [batch_size, n_step] => [batch_size, n_step, m]
    X = X.view(-1, n_step * m) # [batch_size, n_step * m]
    hidden_out = torch.tanh(self.d + torch.mm(X, self.H)) # [batch_size, n_hidden]
    output = self.b + torch.mm(X, self.W) + torch.mm(hidden_out, self.U) # [batch_size, n_class]
    return output
model = NNLM()
criterion = nn.CrossEntropyLoss()
optimizer = optim.Adam(model.parameters(), lr=1e-3)

 

nn.Parameter()
的作用是将该参数添加进模型中,使其能够通过 model.parameters()
找到、管理、并且更新。更具体的来说就是:

 

nn.Parameter()

nn.Module

    1. 一起使用时会有一些特殊的属性,其会被自动加到 Module 的

parameters()

    1. 迭代器中

 

    1. 使用很简单:

torch.nn.Parameter(data, requires_grad=True)

    1. ,其中data为tensor

 

 

简单解释一下执行 X=self.C(X)
这一步之后 X
发生了什幺变化,假设初始 X=[[0, 1], [0, 3]]

 

通过 Embedding()
之后,会将每一个词的索引,替换为对应的词向量,例如 love
这个词的索引是 3
,通过查询Word Embedding表得到行索引为3的向量为 [0.2, 0.1]
,于是就会将原来 X
3
的值替换为该向量,所有值都替换完之后, X=[[[0.3, 0.8], [0.2, 0.4]], [[0.3, 0.8], [0.2, 0.1]]]

 

# Training
for epoch in range(5000):
  for batch_x, batch_y in loader:
    optimizer.zero_grad()
    output = model(batch_x)
    # output : [batch_size, n_class], batch_y : [batch_size] (LongTensor, not one-hot)
    loss = criterion(output, batch_y)
    if (epoch + 1)%1000 == 0:
        print('Epoch:', '%04d' % (epoch + 1), 'cost =', '{:.6f}'.format(loss))
    loss.backward()
    optimizer.step()
# Predict
predict = model(input_batch).data.max(1, keepdim=True)[1]
# Test
print([sen.split()[:n_step] for sen in sentences], '->', [number_dict[n.item()] for n in predict.squeeze()])

 

完整代码:

 

# code by Tae Hwan Jung @graykode, modify by wmathor
import torch
import torch.nn as nn
import torch.optim as optim
import torch.utils.data as Data
dtype = torch.FloatTensor
sentences = [ "i like dog", "i love coffee", "i hate milk"]
word_list = " ".join(sentences).split() # ['i', 'like', 'dog', 'dog', 'i', 'love', 'coffee', 'i', 'hate', 'milk']
word_list = list(set(word_list)) # ['i', 'like', 'dog', 'love', 'coffee', 'hate', 'milk']
word_dict = {w: i for i, w in enumerate(word_list)} # {'i':0, 'like':1, 'dog':2, 'love':3, 'coffee':4, 'hate':5, 'milk':6}
number_dict = {i: w for i, w in enumerate(word_list)} # {0:'i', 1:'like', 2:'dog', 3:'love', 4:'coffee', 5:'hate', 6:'milk'}
n_class = len(word_dict) # number of Vocabulary, just like |V|, in this task n_class=7
# NNLM(Neural Network Language Model) Parameter
n_step = len(sentences[0].split())-1 # n-1 in paper, look back n_step words and predict next word. In this task n_step=2
n_hidden = 2 # h in paper
m = 2 # m in paper, word embedding dim
def make_batch(sentences):
  input_batch = []
  target_batch = []
  for sen in sentences:
    word = sen.split()
    input = [word_dict[n] for n in word[:-1]] # [0, 1], [0, 3], [0, 5]
    target = word_dict[word[-1]] # 2, 4, 6
    input_batch.append(input) # [[0, 1], [0, 3], [0, 5]]
    target_batch.append(target) # [2, 4, 6]
  return input_batch, target_batch
input_batch, target_batch = make_batch(sentences)
input_batch = torch.LongTensor(input_batch)
target_batch = torch.LongTensor(target_batch)
dataset = Data.TensorDataset(input_batch, target_batch)
loader = Data.DataLoader(dataset=dataset, batch_size=16, shuffle=True)
class NNLM(nn.Module):
  def __init__(self):
    super(NNLM, self).__init__()
    self.C = nn.Embedding(n_class, m)
    self.H = nn.Parameter(torch.randn(n_step * m, n_hidden).type(dtype))
    self.W = nn.Parameter(torch.randn(n_step * m, n_class).type(dtype))
    self.d = nn.Parameter(torch.randn(n_hidden).type(dtype))
    self.U = nn.Parameter(torch.randn(n_hidden, n_class).type(dtype))
    self.b = nn.Parameter(torch.randn(n_class).type(dtype))
  def forward(self, X):
    '''
    X: [batch_size, n_step]
    '''
    X = self.C(X) # [batch_size, n_step] => [batch_size, n_step, m]
    X = X.view(-1, n_step * m) # [batch_size, n_step * m]
    hidden_out = torch.tanh(self.d + torch.mm(X, self.H)) # [batch_size, n_hidden]
    output = self.b + torch.mm(X, self.W) + torch.mm(hidden_out, self.U) # [batch_size, n_class]
    return output
model = NNLM()
criterion = nn.CrossEntropyLoss()
optimizer = optim.Adam(model.parameters(), lr=1e-3)
# Training
for epoch in range(5000):
  for batch_x, batch_y in loader:
    optimizer.zero_grad()
    output = model(batch_x)
    # output : [batch_size, n_class], batch_y : [batch_size] (LongTensor, not one-hot)
    loss = criterion(output, batch_y)
    if (epoch + 1)%1000 == 0:
        print('Epoch:', '%04d' % (epoch + 1), 'cost =', '{:.6f}'.format(loss))
    loss.backward()
    optimizer.step()
# Predict
predict = model(input_batch).data.max(1, keepdim=True)[1]
# Test
print([sen.split()[:n_step] for sen in sentences], '->', [number_dict[n.item()] for n in predict.squeeze()])

 

这个代码一开始是在GitHub的一个项目中给出的,下面参考文献给出了链接,代码本身写的没有问题,但是其中有一行注释有问题,就是 X=X.view(-1, n_step*m)
后面的注释,我很确信我写的是正确的。下面两篇参考文献都是一样的错误,需要注意一下

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