循环神经网络

文章目录

python 复制代码
!nvidia-smi
Wed Sep 11 07:23:53 2024       
+-----------------------------------------------------------------------------------------+
| NVIDIA-SMI 550.90.07              Driver Version: 550.90.07      CUDA Version: 12.4     |
|-----------------------------------------+------------------------+----------------------+
| GPU  Name                 Persistence-M | Bus-Id          Disp.A | Volatile Uncorr. ECC |
| Fan  Temp   Perf          Pwr:Usage/Cap |           Memory-Usage | GPU-Util  Compute M. |
|                                         |                        |               MIG M. |
|=========================================+========================+======================|
|   0  Tesla T4                       Off |   00000000:00:04.0 Off |                    0 |
| N/A   36C    P8              9W /   70W |       1MiB /  15360MiB |      0%      Default |
|                                         |                        |                  N/A |
+-----------------------------------------+------------------------+----------------------+
|   1  Tesla T4                       Off |   00000000:00:05.0 Off |                    0 |
| N/A   36C    P8             10W /   70W |       1MiB /  15360MiB |      0%      Default |
|                                         |                        |                  N/A |
+-----------------------------------------+------------------------+----------------------+
                                                                                         
+-----------------------------------------------------------------------------------------+
| Processes:                                                                              |
|  GPU   GI   CI        PID   Type   Process name                              GPU Memory |
|        ID   ID                                                               Usage      |
|=========================================================================================|
|  No running processes found                                                             |
+-----------------------------------------------------------------------------------------+
python 复制代码
!pip install d2l

序列模型

python 复制代码
%matplotlib inline
import torch
from torch import nn
from d2l import torch as d2l

T = 1000  # 总共产生1000个点
time = torch.arange(1, T + 1, dtype=torch.float32)
x = torch.sin(0.01 * time) + torch.normal(0, 0.2, (T,))
d2l.plot(time, [x], 'time', 'x', xlim=[1, 1000], figsize=(6, 3))
python 复制代码
tau = 4
features = torch.zeros((T - tau, tau))
for i in range(tau):
    features[:, i] = x[i: T - tau + i]
labels = x[tau:].reshape((-1, 1))

batch_size, n_train = 16, 600
# 只有前n_train个样本用于训练
train_iter = d2l.load_array((features[:n_train], labels[:n_train]),
                            batch_size, is_train=True)
python 复制代码
# 初始化网络权重的函数
def init_weights(m):
    if type(m) == nn.Linear:
        nn.init.xavier_uniform_(m.weight)

# 一个简单的多层感知机
def get_net():
    net = nn.Sequential(nn.Linear(4, 10),
                        nn.ReLU(),
                        nn.Linear(10, 1))
    net.apply(init_weights)
    return net

# 平方损失。注意:MSELoss计算平方误差时不带系数1/2
loss = nn.MSELoss(reduction='none') # reduction='none' 表示计算损失时不对结果进行任何归约(reduction),即不对损失值求和或取平均值。它会返回每个输入数据点对应的损失值,而不是一个标量结果。
python 复制代码
def train(net, train_iter, loss, epochs, lr):
    trainer = torch.optim.Adam(net.parameters(), lr)
    for epoch in range(epochs):
        for X, y in train_iter:
            trainer.zero_grad()
            l = loss(net(X), y)
            l.sum().backward()
            trainer.step()
        print(f'epoch {epoch + 1}, '
              f'loss: {d2l.evaluate_loss(net, train_iter, loss):f}')

net = get_net()
train(net, train_iter, loss, 5, 0.01)
epoch 1, loss: 0.082473
epoch 2, loss: 0.065913
epoch 3, loss: 0.060240
epoch 4, loss: 0.058487
epoch 5, loss: 0.058331
python 复制代码
onestep_preds = net(features)
d2l.plot([time, time[tau:]],
         [x.detach().numpy(), onestep_preds.detach().numpy()], 'time',
         'x', legend=['data', '1-step preds'], xlim=[1, 1000],
         figsize=(6, 3))
python 复制代码
multistep_preds = torch.zeros(T)
multistep_preds[: n_train + tau] = x[: n_train + tau]
for i in range(n_train + tau, T):
    multistep_preds[i] = net(
        multistep_preds[i - tau:i].reshape((1, -1)))

d2l.plot([time, time[tau:], time[n_train + tau:]],
         [x.detach().numpy(), onestep_preds.detach().numpy(),
          multistep_preds[n_train + tau:].detach().numpy()], 'time',
         'x', legend=['data', '1-step preds', 'multistep preds'],
         xlim=[1, 1000], figsize=(6, 3))
python 复制代码
max_steps = 64

features = torch.zeros((T - tau - max_steps + 1, tau + max_steps))
# 列i(i<tau)是来自x的观测,其时间步从(i)到(i+T-tau-max_steps+1)
for i in range(tau):
    features[:, i] = x[i: i + T - tau - max_steps + 1]

# 列i(i>=tau)是来自(i-tau+1)步的预测,其时间步从(i)到(i+T-tau-max_steps+1)
for i in range(tau, tau + max_steps):
    features[:, i] = net(features[:, i - tau:i]).reshape(-1)

steps = (1, 4, 16, 64)
d2l.plot([time[tau + i - 1: T - max_steps + i] for i in steps],
         [features[:, (tau + i - 1)].detach().numpy() for i in steps], 'time', 'x',
         legend=[f'{i}-step preds' for i in steps], xlim=[5, 1000],
         figsize=(6, 3))

文本预处理

python 复制代码
import collections
import re
from d2l import torch as d2l
python 复制代码
d2l.DATA_HUB['time_machine'] = (d2l.DATA_URL + 'timemachine.txt',
                                '090b5e7e70c295757f55df93cb0a180b9691891a')

def read_time_machine(): 
    """将时间机器数据集加载到文本行的列表中"""
    with open(d2l.download('time_machine'), 'r') as f:
        lines = f.readlines()
    return [re.sub('[^A-Za-z]+', ' ', line).strip().lower() for line in lines]

lines = read_time_machine()
print(f'# 文本总行数: {len(lines)}')
print(lines[0])
print(lines[10])
Downloading ../data/timemachine.txt from http://d2l-data.s3-accelerate.amazonaws.com/timemachine.txt...
# 文本总行数: 3221
the time machine by h g wells
twinkled and his usually pale face was flushed and animated the
python 复制代码
def tokenize(lines, token='word'): 
    """将文本行拆分为单词或字符词元"""
    if token == 'word':
        return [line.split() for line in lines]
    elif token == 'char':
        return [list(line) for line in lines]
    else:
        print('错误:未知词元类型:' + token)

tokens = tokenize(lines)
for i in range(11):
    print(tokens[i])
['the', 'time', 'machine', 'by', 'h', 'g', 'wells']
[]
[]
[]
[]
['i']
[]
[]
['the', 'time', 'traveller', 'for', 'so', 'it', 'will', 'be', 'convenient', 'to', 'speak', 'of', 'him']
['was', 'expounding', 'a', 'recondite', 'matter', 'to', 'us', 'his', 'grey', 'eyes', 'shone', 'and']
['twinkled', 'and', 'his', 'usually', 'pale', 'face', 'was', 'flushed', 'and', 'animated', 'the']
python 复制代码
class Vocab: 
    """文本词表"""
    def __init__(self, tokens=None, min_freq=0, reserved_tokens=None):
        if tokens is None:
            tokens = []
        if reserved_tokens is None:
            reserved_tokens = []
        # 按出现频率排序
        counter = count_corpus(tokens)
        self._token_freqs = sorted(counter.items(), key=lambda x: x[1],
                                   reverse=True)
        # 未知词元的索引为0
        self.idx_to_token = ['<unk>'] + reserved_tokens
        self.token_to_idx = {token: idx
                             for idx, token in enumerate(self.idx_to_token)}
        for token, freq in self._token_freqs:
            if freq < min_freq:
                break
            if token not in self.token_to_idx:
                self.idx_to_token.append(token)
                self.token_to_idx[token] = len(self.idx_to_token) - 1

    def __len__(self):
        return len(self.idx_to_token)

    def __getitem__(self, tokens):
        if not isinstance(tokens, (list, tuple)):
            return self.token_to_idx.get(tokens, self.unk)
        return [self.__getitem__(token) for token in tokens]

    def to_tokens(self, indices):
        if not isinstance(indices, (list, tuple)):
            return self.idx_to_token[indices]
        return [self.idx_to_token[index] for index in indices]

    @property
    def unk(self):  # 未知词元的索引为0
        return 0

    @property
    def token_freqs(self):
        return self._token_freqs

def count_corpus(tokens): 
    """统计词元的频率"""
    # 这里的tokens是1D列表或2D列表
    
    if len(tokens) == 0 or isinstance(tokens[0], list):
        # 将词元列表展平成一维列表
        tokens = [token for line in tokens for token in line]
    return collections.Counter(tokens)
python 复制代码
vocab = Vocab(tokens)
print(list(vocab.token_to_idx.items())[:10])
[('<unk>', 0), ('the', 1), ('i', 2), ('and', 3), ('of', 4), ('a', 5), ('to', 6), ('was', 7), ('in', 8), ('that', 9)]
python 复制代码
for i in [0, 10]:
    print('文本:', tokens[i])
    print('索引:', vocab[tokens[i]])
文本: ['the', 'time', 'machine', 'by', 'h', 'g', 'wells']
索引: [1, 19, 50, 40, 2183, 2184, 400]
文本: ['twinkled', 'and', 'his', 'usually', 'pale', 'face', 'was', 'flushed', 'and', 'animated', 'the']
索引: [2186, 3, 25, 1044, 362, 113, 7, 1421, 3, 1045, 1]
python 复制代码
def load_corpus_time_machine(max_tokens=-1):  #@save
    """返回时光机器数据集的词元索引列表和词表"""
    lines = read_time_machine()
    tokens = tokenize(lines, 'char')
    vocab = Vocab(tokens)
    # 因为时光机器数据集中的每个文本行不一定是一个句子或一个段落,
    # 所以将所有文本行展平到一个列表中
    corpus = [vocab[token] for line in tokens for token in line]
    if max_tokens > 0:
        corpus = corpus[:max_tokens]
    return corpus, vocab

corpus, vocab = load_corpus_time_machine()
len(corpus), len(vocab)
(170580, 28)

语言模型和数据集

python 复制代码
import random
import torch
from d2l import torch as d2l

tokens = d2l.tokenize(read_time_machine())
# 因为每个文本行不一定是一个句子或一个段落,因此我们把所有文本行拼接到一起
corpus = [token for line in tokens for token in line]
vocab = d2l.Vocab(corpus)
vocab.token_freqs[:10]
[('the', 2261),
 ('i', 1267),
 ('and', 1245),
 ('of', 1155),
 ('a', 816),
 ('to', 695),
 ('was', 552),
 ('in', 541),
 ('that', 443),
 ('my', 440)]
python 复制代码
freqs = [freq for token, freq in vocab.token_freqs]
d2l.plot(freqs, xlabel='token: x', ylabel='frequency: n(x)',
         xscale='log', yscale='log')
python 复制代码
bigram_tokens = [pair for pair in zip(corpus[:-1], corpus[1:])]
bigram_vocab = Vocab(bigram_tokens)
bigram_vocab.token_freqs[:10]
[(('of', 'the'), 309),
 (('in', 'the'), 169),
 (('i', 'had'), 130),
 (('i', 'was'), 112),
 (('and', 'the'), 109),
 (('the', 'time'), 102),
 (('it', 'was'), 99),
 (('to', 'the'), 85),
 (('as', 'i'), 78),
 (('of', 'a'), 73)]
python 复制代码
trigram_tokens = [triple for triple in zip(
    corpus[:-2], corpus[1:-1], corpus[2:])]
trigram_vocab = Vocab(trigram_tokens)
trigram_vocab.token_freqs[:10]
[(('the', 'time', 'traveller'), 59),
 (('the', 'time', 'machine'), 30),
 (('the', 'medical', 'man'), 24),
 (('it', 'seemed', 'to'), 16),
 (('it', 'was', 'a'), 15),
 (('here', 'and', 'there'), 15),
 (('seemed', 'to', 'me'), 14),
 (('i', 'did', 'not'), 14),
 (('i', 'saw', 'the'), 13),
 (('i', 'began', 'to'), 13)]
python 复制代码
bigram_freqs = [freq for token, freq in bigram_vocab.token_freqs]
trigram_freqs = [freq for token, freq in trigram_vocab.token_freqs]
d2l.plot([freqs, bigram_freqs, trigram_freqs], xlabel='token: x',
         ylabel='frequency: n(x)', xscale='log', yscale='log',
         legend=['unigram', 'bigram', 'trigram'])
python 复制代码
def seq_data_iter_random(corpus, batch_size, num_steps):  #@save
    """使用随机抽样生成一个小批量子序列"""
    # 从随机偏移量开始对序列进行分区,随机范围包括num_steps-1
    corpus = corpus[random.randint(0, num_steps - 1):]
    # 减去1,是因为我们需要考虑标签
    num_subseqs = (len(corpus) - 1) // num_steps
    # 长度为num_steps的子序列的起始索引
    initial_indices = list(range(0, num_subseqs * num_steps, num_steps))
    # 在随机抽样的迭代过程中,
    # 来自两个相邻的、随机的、小批量中的子序列不一定在原始序列上相邻
    random.shuffle(initial_indices)

    def data(pos):
        # 返回从pos位置开始的长度为num_steps的序列
        return corpus[pos: pos + num_steps]

    num_batches = num_subseqs // batch_size
    for i in range(0, batch_size * num_batches, batch_size):
        # 在这里,initial_indices包含子序列的随机起始索引
        initial_indices_per_batch = initial_indices[i: i + batch_size]
        X = [data(j) for j in initial_indices_per_batch]
        Y = [data(j + 1) for j in initial_indices_per_batch]
        yield torch.tensor(X), torch.tensor(Y)
python 复制代码
my_seq = list(range(35))
for X, Y in seq_data_iter_random(my_seq, batch_size=2, num_steps=5):
    print('X: ', X, '\nY:', Y)
X:  tensor([[ 9, 10, 11, 12, 13],
        [14, 15, 16, 17, 18]]) 
Y: tensor([[10, 11, 12, 13, 14],
        [15, 16, 17, 18, 19]])
X:  tensor([[29, 30, 31, 32, 33],
        [19, 20, 21, 22, 23]]) 
Y: tensor([[30, 31, 32, 33, 34],
        [20, 21, 22, 23, 24]])
X:  tensor([[24, 25, 26, 27, 28],
        [ 4,  5,  6,  7,  8]]) 
Y: tensor([[25, 26, 27, 28, 29],
        [ 5,  6,  7,  8,  9]])
python 复制代码
def seq_data_iter_sequential(corpus, batch_size, num_steps):  #@save
    """使用顺序分区生成一个小批量子序列"""
    # 从随机偏移量开始划分序列
    offset = random.randint(0, num_steps)
    num_tokens = ((len(corpus) - offset - 1) // batch_size) * batch_size
    Xs = torch.tensor(corpus[offset: offset + num_tokens])
    Ys = torch.tensor(corpus[offset + 1: offset + 1 + num_tokens])
    Xs, Ys = Xs.reshape(batch_size, -1), Ys.reshape(batch_size, -1)
    num_batches = Xs.shape[1] // num_steps
    for i in range(0, num_steps * num_batches, num_steps):
        X = Xs[:, i: i + num_steps]
        Y = Ys[:, i: i + num_steps]
        yield X, Y
python 复制代码
for X, Y in seq_data_iter_sequential(my_seq, batch_size=2, num_steps=4):
    print('X: ', X, '\nY:', Y)
X:  tensor([[ 3,  4,  5,  6],
        [18, 19, 20, 21]]) 
Y: tensor([[ 4,  5,  6,  7],
        [19, 20, 21, 22]])
X:  tensor([[ 7,  8,  9, 10],
        [22, 23, 24, 25]]) 
Y: tensor([[ 8,  9, 10, 11],
        [23, 24, 25, 26]])
X:  tensor([[11, 12, 13, 14],
        [26, 27, 28, 29]]) 
Y: tensor([[12, 13, 14, 15],
        [27, 28, 29, 30]])
python 复制代码
class SeqDataLoader: 
    """加载序列数据的迭代器"""
    def __init__(self, batch_size, num_steps, use_random_iter, max_tokens):
        if use_random_iter:
            self.data_iter_fn = seq_data_iter_random
        else:
            self.data_iter_fn = seq_data_iter_sequential
        self.corpus, self.vocab = load_corpus_time_machine(max_tokens)
        self.batch_size, self.num_steps = batch_size, num_steps

    def __iter__(self):
        return self.data_iter_fn(self.corpus, self.batch_size, self.num_steps)
python 复制代码
def load_data_time_machine(batch_size, num_steps,  #@save
                           use_random_iter=False, max_tokens=10000):
    """返回时光机器数据集的迭代器和词表"""
    data_iter = SeqDataLoader(
        batch_size, num_steps, use_random_iter, max_tokens)
    return data_iter, data_iter.vocab

循环神经网络

python 复制代码
import torch

X, W_xh = torch.randn(3, 1), torch.randn(1, 4)
H, W_hh = torch.randn(3, 4), torch.randn(4, 4)
torch.matmul(X, W_xh) + torch.matmul(H, W_hh)
tensor([[ 1.5182,  1.9115, -0.0618,  0.0826],
        [-0.3502,  4.0483,  0.9087, -0.2270],
        [ 0.7328, -0.7081,  0.9375, -1.7978]])
python 复制代码
torch.matmul(torch.cat((X, H), dim=1), torch.cat((W_xh, W_hh), dim=0))
tensor([[ 1.5182,  1.9115, -0.0618,  0.0826],
        [-0.3502,  4.0483,  0.9087, -0.2270],
        [ 0.7328, -0.7081,  0.9375, -1.7978]])

从0实现

python 复制代码
%matplotlib inline
import math
import torch
from torch import nn
from torch.nn import functional as F
from d2l import torch as d2l

batch_size, num_steps = 32, 35
train_iter, vocab = load_data_time_machine(batch_size, num_steps)
python 复制代码
F.one_hot(torch.tensor([0, 2]), len(vocab))
tensor([[1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
         0, 0, 0, 0],
        [0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
         0, 0, 0, 0]])
python 复制代码
X = torch.arange(10).reshape((2, 5))
F.one_hot(X.T, 28).shape
torch.Size([5, 2, 28])
python 复制代码
def get_params(vocab_size, num_hiddens, device):
    num_inputs = num_outputs = vocab_size

    def normal(shape):
        return torch.randn(size=shape, device=device) * 0.01

    # 隐藏层参数
    W_xh = normal((num_inputs, num_hiddens))
    W_hh = normal((num_hiddens, num_hiddens))
    b_h = torch.zeros(num_hiddens, device=device)
    # 输出层参数
    W_hq = normal((num_hiddens, num_outputs))
    b_q = torch.zeros(num_outputs, device=device)
    # 附加梯度
    params = [W_xh, W_hh, b_h, W_hq, b_q]
    for param in params:
        param.requires_grad_(True)
    return params
python 复制代码
def init_rnn_state(batch_size, num_hiddens, device):
    return (torch.zeros((batch_size, num_hiddens), device=device), )
python 复制代码
def rnn(inputs, state, params):
    # inputs的形状:(时间步数量,批量大小,词表大小)
    W_xh, W_hh, b_h, W_hq, b_q = params
    H, = state
    outputs = []
    # X的形状:(批量大小,词表大小)
    for X in inputs:
        H = torch.tanh(torch.mm(X, W_xh) + torch.mm(H, W_hh) + b_h)
        Y = torch.mm(H, W_hq) + b_q
        outputs.append(Y)
    return torch.cat(outputs, dim=0), (H,)
# 第一个返回值是模型在所有时间步上的输出序列,形状为(时间步数 × 批量大小, 输出维度)。
# 第二个返回值是最终的隐藏状态H,以便后续使用。
python 复制代码
class RNNModelScratch: #@save
    """从零开始实现的循环神经网络模型"""
    def __init__(self, vocab_size, num_hiddens, device,
                 get_params, init_state, forward_fn):
        self.vocab_size, self.num_hiddens = vocab_size, num_hiddens
        self.params = get_params(vocab_size, num_hiddens, device)
        self.init_state, self.forward_fn = init_state, forward_fn

    def __call__(self, X, state):
        X = F.one_hot(X.T, self.vocab_size).type(torch.float32)
        return self.forward_fn(X, state, self.params)

    def begin_state(self, batch_size, device):
        return self.init_state(batch_size, self.num_hiddens, device)
python 复制代码
num_hiddens = 512
net = RNNModelScratch(len(vocab), num_hiddens, d2l.try_gpu(), get_params,
                      init_rnn_state, rnn)
state = net.begin_state(X.shape[0], d2l.try_gpu())
Y, new_state = net(X.to(d2l.try_gpu()), state)
Y.shape, len(new_state), new_state[0].shape
(torch.Size([10, 28]), 1, torch.Size([2, 512]))
python 复制代码
def predict_ch8(prefix, num_preds, net, vocab, device):  #@save
    """在prefix后面生成新字符"""
    state = net.begin_state(batch_size=1, device=device)
    outputs = [vocab[prefix[0]]]
    get_input = lambda: torch.tensor([outputs[-1]], device=device).reshape((1, 1))
    for y in prefix[1:]:  # 预热期
        _, state = net(get_input(), state)
        outputs.append(vocab[y])
    for _ in range(num_preds):  # 预测num_preds步
        y, state = net(get_input(), state)
        outputs.append(int(y.argmax(dim=1).reshape(1)))
    return ''.join([vocab.idx_to_token[i] for i in outputs])
python 复制代码
predict_ch8('time traveller ', 10, net, vocab, d2l.try_gpu())
'time traveller avavavavav'
python 复制代码
def grad_clipping(net, theta):  #@save
    """裁剪梯度"""
    if isinstance(net, nn.Module):
        params = [p for p in net.parameters() if p.requires_grad]
    else:
        params = net.params
    norm = torch.sqrt(sum(torch.sum((p.grad ** 2)) for p in params))
    if norm > theta:
        for param in params:
            param.grad[:] *= theta / norm
python 复制代码
#@save
def train_epoch_ch8(net, train_iter, loss, updater, device, use_random_iter):
    """训练网络一个迭代周期(定义见第8章)"""
    state, timer = None, d2l.Timer()
    metric = d2l.Accumulator(2)  # 训练损失之和,词元数量
    for X, Y in train_iter:
        if state is None or use_random_iter:
            # 在第一次迭代或使用随机抽样时初始化state
            state = net.begin_state(batch_size=X.shape[0], device=device)
        else:
            if isinstance(net, nn.Module) and not isinstance(state, tuple):
                # state对于nn.GRU是个张量
                state.detach_()
            else:
                # state对于nn.LSTM或对于我们从零开始实现的模型是个张量
                for s in state:
                    s.detach_()
        y = Y.T.reshape(-1)
        X, y = X.to(device), y.to(device)
        y_hat, state = net(X, state)
        l = loss(y_hat, y.long()).mean()
        if isinstance(updater, torch.optim.Optimizer):
            updater.zero_grad()
            l.backward()
            grad_clipping(net, 1)
            updater.step()
        else:
            l.backward()
            grad_clipping(net, 1)
            # 因为已经调用了mean函数
            updater(batch_size=1)
        metric.add(l * y.numel(), y.numel())
    return math.exp(metric[0] / metric[1]), metric[1] / timer.stop()
python 复制代码
#@save
def train_ch8(net, train_iter, vocab, lr, num_epochs, device,
              use_random_iter=False):
    """训练模型(定义见第8章)"""
    loss = nn.CrossEntropyLoss()
    animator = d2l.Animator(xlabel='epoch', ylabel='perplexity',
                            legend=['train'], xlim=[10, num_epochs])
    # 初始化
    if isinstance(net, nn.Module):
        updater = torch.optim.SGD(net.parameters(), lr)
    else:
        updater = lambda batch_size: d2l.sgd(net.params, lr, batch_size)
    predict = lambda prefix: predict_ch8(prefix, 50, net, vocab, device)
    # 训练和预测
    for epoch in range(num_epochs):
        ppl, speed = train_epoch_ch8(
            net, train_iter, loss, updater, device, use_random_iter)
        if (epoch + 1) % 10 == 0:
            print(predict('time traveller'))
            animator.add(epoch + 1, [ppl])
    print(f'困惑度 {ppl:.1f}, {speed:.1f} 词元/秒 {str(device)}')
    print(predict('time traveller'))
    print(predict('traveller'))
python 复制代码
# num_epochs, lr = 500, 1
# train_ch8(net, train_iter, vocab, lr, num_epochs, d2l.try_gpu())
python 复制代码
# net = RNNModelScratch(len(vocab), num_hiddens, d2l.try_gpu(), get_params,
#                       init_rnn_state, rnn)
# train_ch8(net, train_iter, vocab, lr, num_epochs, d2l.try_gpu(),
#           use_random_iter=True)

简洁实现

python 复制代码
import torch
from torch import nn
from torch.nn import functional as F
from d2l import torch as d2l

batch_size, num_steps = 32, 35
train_iter, vocab = load_data_time_machine(batch_size, num_steps)
python 复制代码
num_hiddens = 256
rnn_layer = nn.RNN(len(vocab), num_hiddens)
python 复制代码
state = torch.zeros((1, batch_size, num_hiddens))
state.shape
torch.Size([1, 32, 256])
python 复制代码
X = torch.rand(size=(num_steps, batch_size, len(vocab)))
Y, state_new = rnn_layer(X, state)
Y.shape, state_new.shape
(torch.Size([35, 32, 256]), torch.Size([1, 32, 256]))
python 复制代码
class RNNModel(nn.Module):
    """循环神经网络模型"""
    def __init__(self, rnn_layer, vocab_size, **kwargs):
        super(RNNModel, self).__init__(**kwargs)
        self.rnn = rnn_layer
        self.vocab_size = vocab_size
        self.num_hiddens = self.rnn.hidden_size
        # 如果RNN是双向的(之后将介绍),num_directions应该是2,否则应该是1
        if not self.rnn.bidirectional:
            self.num_directions = 1
            self.linear = nn.Linear(self.num_hiddens, self.vocab_size)
        else:
            self.num_directions = 2
            self.linear = nn.Linear(self.num_hiddens * 2, self.vocab_size)

    def forward(self, inputs, state):
        X = F.one_hot(inputs.T.long(), self.vocab_size)
        X = X.to(torch.float32)
        Y, state = self.rnn(X, state)
        # 全连接层首先将Y的形状改为(时间步数*批量大小,隐藏单元数)
        # 它的输出形状是(时间步数*批量大小,词表大小)。
        output = self.linear(Y.reshape((-1, Y.shape[-1])))
        return output, state

    def begin_state(self, device, batch_size=1):
        if not isinstance(self.rnn, nn.LSTM):
            # nn.GRU以张量作为隐状态
            return  torch.zeros((self.num_directions * self.rnn.num_layers,
                                 batch_size, self.num_hiddens),
                                device=device)
        else:
            # nn.LSTM以元组作为隐状态
            return (torch.zeros((
                self.num_directions * self.rnn.num_layers,
                batch_size, self.num_hiddens), device=device),
                    torch.zeros((
                        self.num_directions * self.rnn.num_layers,
                        batch_size, self.num_hiddens), device=device))
python 复制代码
# device = d2l.try_gpu()
# net = RNNModel(rnn_layer, vocab_size=len(vocab))
# net = net.to(device)
# num_epochs, lr = 500, 1
# # predict_ch8('time traveller', 10, net, vocab, device)
# train_ch8(net, train_iter, vocab, lr, num_epochs, device)

GRU

从0开始实现

python 复制代码
import torch
from torch import nn
from d2l import torch as d2l

batch_size, num_steps = 32, 35
train_iter, vocab = load_data_time_machine(batch_size, num_steps)
python 复制代码
def get_params(vocab_size, num_hiddens, device):
    num_inputs = num_outputs = vocab_size

    def normal(shape):
        return torch.randn(size=shape, device=device)*0.01

    def three():
        return (normal((num_inputs, num_hiddens)),
                normal((num_hiddens, num_hiddens)),
                torch.zeros(num_hiddens, device=device))

    W_xz, W_hz, b_z = three()  # 更新门参数
    W_xr, W_hr, b_r = three()  # 重置门参数
    W_xh, W_hh, b_h = three()  # 候选隐状态参数
    # 输出层参数
    W_hq = normal((num_hiddens, num_outputs))
    b_q = torch.zeros(num_outputs, device=device)
    # 附加梯度
    params = [W_xz, W_hz, b_z, W_xr, W_hr, b_r, W_xh, W_hh, b_h, W_hq, b_q]
    for param in params:
        param.requires_grad_(True)
    return params
python 复制代码
def init_gru_state(batch_size, num_hiddens, device):
    return (torch.zeros((batch_size, num_hiddens), device=device), )
python 复制代码
def gru(inputs, state, params):
    W_xz, W_hz, b_z, W_xr, W_hr, b_r, W_xh, W_hh, b_h, W_hq, b_q = params
    H, = state
    outputs = []
    for X in inputs:
        Z = torch.sigmoid((X @ W_xz) + (H @ W_hz) + b_z)
        R = torch.sigmoid((X @ W_xr) + (H @ W_hr) + b_r)
        H_tilda = torch.tanh((X @ W_xh) + ((R * H) @ W_hh) + b_h)
        H = Z * H + (1 - Z) * H_tilda
        Y = H @ W_hq + b_q
        outputs.append(Y)
    return torch.cat(outputs, dim=0), (H,)
python 复制代码
# 运行较久,不运行了
# vocab_size, num_hiddens, device = len(vocab), 256, d2l.try_gpu()
# num_epochs, lr = 500, 1
# model = RNNModelScratch(len(vocab), num_hiddens, device, get_params,
#                             init_gru_state, gru)
# train_ch8(model, train_iter, vocab, lr, num_epochs, device)

简洁实现

python 复制代码
# num_inputs = vocab_size
# gru_layer = nn.GRU(num_inputs, num_hiddens)
# model = RNNModel(gru_layer, len(vocab))
# model = model.to(device)
# train_ch8(model, train_iter, vocab, lr, num_epochs, device)

一个例子

python 复制代码
import torch

# 1、确定参数
seq_len = 5
input_size = 4
hidden_size = 4
batch_size = 1

# 2、准备数据
index2char = ['e', 'h', 'l', 'o']  #字典
x_data = [1, 0, 2, 2, 3]  #用字典中的索引(数字)表示来表示hello
y_data = [3, 1, 2, 3, 2]  #标签:ohlol

one_hot_lookup = [[1, 0, 0, 0],  # 用来将x_data转换为one-hot向量的参照表
                  [0, 1, 0, 0],
                  [0, 0, 1, 0],
                  [0, 0, 0, 1]]
x_one_hot = [one_hot_lookup[x] for x in x_data]  #将x_data转换为one-hot向量
inputs = torch.Tensor(x_one_hot).view(seq_len, batch_size,
                                      input_size)  #(𝒔𝒆𝒒𝑳𝒆𝒏,𝒃𝒂𝒕𝒄𝒉𝑺𝒊𝒛𝒆,𝒊𝒏𝒑𝒖𝒕𝑺𝒊𝒛𝒆)
labels = torch.LongTensor(y_data)
inputs,labels
(tensor([[[0., 1., 0., 0.]],
 
         [[1., 0., 0., 0.]],
 
         [[0., 0., 1., 0.]],
 
         [[0., 0., 1., 0.]],
 
         [[0., 0., 0., 1.]]]),
 tensor([3, 1, 2, 3, 2]))
python 复制代码
# 3、构建模型
class Model(torch.nn.Module):
    def __init__(self, input_size, hidden_size, batch_size, num_layers=1):
        super(Model, self).__init__()
        self.num_layers = num_layers
        self.batch_size = batch_size
        self.input_size = input_size
        self.hidden_size = hidden_size
        self.rnn = torch.nn.RNN(input_size=self.input_size, hidden_size=self.hidden_size, num_layers=num_layers)

    def forward(self, input):
        hidden = torch.zeros(self.num_layers, self.batch_size, self.hidden_size)
        out, _ = self.rnn(input, hidden)  # out: tensor of shape (seq_len, batch, hidden_size)
        return out.view(-1, self.hidden_size)  # 将输出的三维张量转换为二维张量,(𝒔𝒆𝒒𝑳𝒆𝒏×𝒃𝒂𝒕𝒄𝒉𝑺𝒊𝒛𝒆,𝒉𝒊𝒅𝒅𝒆𝒏𝑺𝒊𝒛𝒆)

    def init_hidden(self):  #初始化隐藏层,需要batch_size
        return torch.zeros(self.batch_size, self.hidden_size)


net = Model(input_size, hidden_size, batch_size)

# 4、损失和优化器
criterion = torch.nn.CrossEntropyLoss()
optimizer = torch.optim.Adam(net.parameters(), lr=0.05)  # Adam优化器

# 5、训练
for epoch in range(100):
    optimizer.zero_grad()
    outputs = net(inputs)
    loss = criterion(outputs, labels)
    loss.backward()
    optimizer.step()

    _, idx = outputs.max(dim=1)
    idx = idx.data.numpy()
    print('Predicted string: ', ''.join([index2char[x] for x in idx]), end='')
    print(', Epoch [%d/15] loss: %.4f' % (epoch + 1, loss.item()))
Predicted string:  hohhl, Epoch [1/15] loss: 1.2648
Predicted string:  oolll, Epoch [2/15] loss: 1.1561
Predicted string:  oolll, Epoch [3/15] loss: 1.0815
Predicted string:  ollll, Epoch [4/15] loss: 1.0268
Predicted string:  ollll, Epoch [5/15] loss: 0.9794
Predicted string:  oolll, Epoch [6/15] loss: 0.9351
Predicted string:  ohlll, Epoch [7/15] loss: 0.8946
Predicted string:  ohlll, Epoch [8/15] loss: 0.8583
Predicted string:  ohlol, Epoch [9/15] loss: 0.8252
Predicted string:  ohlol, Epoch [10/15] loss: 0.7928
Predicted string:  ohlol, Epoch [11/15] loss: 0.7594
Predicted string:  ohlol, Epoch [12/15] loss: 0.7247


Predicted string:  ohlol, Epoch [97/15] loss: 0.3466
Predicted string:  ohlol, Epoch [98/15] loss: 0.3465
Predicted string:  ohlol, Epoch [99/15] loss: 0.3465
Predicted string:  ohlol, Epoch [100/15] loss: 0.3464

LSTM

从0实现

python 复制代码
import torch
from torch import nn
from d2l import torch as d2l

batch_size, num_steps = 32, 35
train_iter, vocab = load_data_time_machine(batch_size, num_steps)
python 复制代码
def get_lstm_params(vocab_size, num_hiddens, device):
    num_inputs = num_outputs = vocab_size

    def normal(shape):
        return torch.randn(size=shape, device=device)*0.01

    def three():
        return (normal((num_inputs, num_hiddens)),
                normal((num_hiddens, num_hiddens)),
                torch.zeros(num_hiddens, device=device))

    W_xi, W_hi, b_i = three()  # 输入门参数
    W_xf, W_hf, b_f = three()  # 遗忘门参数
    W_xo, W_ho, b_o = three()  # 输出门参数
    W_xc, W_hc, b_c = three()  # 候选记忆元参数
    # 输出层参数
    W_hq = normal((num_hiddens, num_outputs))
    b_q = torch.zeros(num_outputs, device=device)
    # 附加梯度
    params = [W_xi, W_hi, b_i, W_xf, W_hf, b_f, W_xo, W_ho, b_o, W_xc, W_hc,
              b_c, W_hq, b_q]
    for param in params:
        param.requires_grad_(True)
    return params
python 复制代码
def init_lstm_state(batch_size, num_hiddens, device):
    return (torch.zeros((batch_size, num_hiddens), device=device),
            torch.zeros((batch_size, num_hiddens), device=device))
python 复制代码
def lstm(inputs, state, params):
    # 将参数 params 分解为各个权重和偏置矩阵
    [W_xi, W_hi, b_i,  # 输入门的权重和偏置
     W_xf, W_hf, b_f,  # 遗忘门的权重和偏置
     W_xo, W_ho, b_o,  # 输出门的权重和偏置
     W_xc, W_hc, b_c,  # 记忆单元的权重和偏置
     W_hq, b_q] = params  # 最后的输出层权重和偏置

    (H, C) = state  # 当前的隐藏状态 (H) 和记忆状态 (C)
    outputs = []  # 用于存储输出
    
    # 遍历每一个时间步的输入
    for X in inputs:
        # 输入门计算,决定是否更新记忆单元
        I = torch.sigmoid((X @ W_xi) + (H @ W_hi) + b_i)  
        
        # 遗忘门计算,决定是否忘记之前的记忆
        F = torch.sigmoid((X @ W_xf) + (H @ W_hf) + b_f)  
        
        # 输出门计算,决定从记忆单元输出多少
        O = torch.sigmoid((X @ W_xo) + (H @ W_ho) + b_o)  
        
        # 候选记忆单元 C_tilda,使用 tanh 激活函数生成新的记忆
        C_tilda = torch.tanh((X @ W_xc) + (H @ W_hc) + b_c)  
        
        # 更新记忆单元 C,结合遗忘门的输出 F 和输入门的输出 I 及 C_tilda
        C = F * C + I * C_tilda  
        
        # 更新隐藏状态 H,结合输出门 O 和当前记忆单元 C
        H = O * torch.tanh(C)  
        
        # 输出层的计算,H 投影到输出 Y
        Y = (H @ W_hq) + b_q  
        
        # 保存当前时间步的输出 Y
        outputs.append(Y)

    # 返回所有时间步的输出,拼接成一个完整的输出序列,以及最后的隐藏状态和记忆状态
    return torch.cat(outputs, dim=0), (H, C)
python 复制代码
# vocab_size, num_hiddens, device = len(vocab), 256, d2l.try_gpu()
# num_epochs, lr = 500, 1
# model = RNNModelScratch(len(vocab), num_hiddens, device, get_lstm_params,
#                             init_lstm_state, lstm)
# train_ch8(model, train_iter, vocab, lr, num_epochs, device)

简洁实现

python 复制代码
# num_inputs = vocab_size
# lstm_layer = nn.LSTM(num_inputs, num_hiddens)
# model = RNNModel(lstm_layer, len(vocab))
# model = model.to(device)
# train_ch8(model, train_iter, vocab, lr, num_epochs, device)

深度循环神经网络

python 复制代码
import torch
from torch import nn
from d2l import torch as d2l

batch_size, num_steps = 32, 35
train_iter, vocab = load_data_time_machine(batch_size, num_steps)
python 复制代码
vocab_size, num_hiddens, num_layers = len(vocab), 256, 2
num_inputs = vocab_size
device = d2l.try_gpu()
lstm_layer = nn.LSTM(num_inputs, num_hiddens, num_layers)
model = RNNModel(lstm_layer, len(vocab))
model = model.to(device)
python 复制代码
# num_epochs, lr = 500, 2
# train_ch8(model, train_iter, vocab, lr*1.0, num_epochs, device)

双向循环神经网络

python 复制代码
# import torch
# from torch import nn
# from d2l import torch as d2l

# # 加载数据
# batch_size, num_steps, device = 32, 35, d2l.try_gpu()
# train_iter, vocab = load_data_time_machine(batch_size, num_steps)
# # 通过设置"bidirective=True"来定义双向LSTM模型
# vocab_size, num_hiddens, num_layers = len(vocab), 256, 2
# num_inputs = vocab_size
# lstm_layer = nn.LSTM(num_inputs, num_hiddens, num_layers, bidirectional=True)
# model = RNNModel(lstm_layer, len(vocab))
# model = model.to(device)
# # 训练模型
# num_epochs, lr = 500, 1
# train_ch8(model, train_iter, vocab, lr, num_epochs, device)

机器翻译与数据集

python 复制代码
import os
import torch
from d2l import torch as d2l
python 复制代码
#@save
d2l.DATA_HUB['fra-eng'] = (d2l.DATA_URL + 'fra-eng.zip',
                           '94646ad1522d915e7b0f9296181140edcf86a4f5')

#@save
def read_data_nmt():
    """载入"英语-法语"数据集"""
    data_dir = d2l.download_extract('fra-eng')
    with open(os.path.join(data_dir, 'fra.txt'), 'r',
             encoding='utf-8') as f:
        return f.read()

raw_text = read_data_nmt()
print(raw_text[:75])
Downloading ../data/fra-eng.zip from http://d2l-data.s3-accelerate.amazonaws.com/fra-eng.zip...
Go.	Va !
Hi.	Salut !
Run!	Cours !
Run!	Courez !
Who?	Qui ?
Wow!	Ça alors !
python 复制代码
#@save
def preprocess_nmt(text):
    """预处理"英语-法语"数据集"""
    def no_space(char, prev_char):
        return char in set(',.!?') and prev_char != ' '

    # 使用普通空格替换不间断空格:为了确保文本的一致性、简化处理流程,并减少潜在的兼容性和显示问题
    text = text.replace('\u202f', ' ').replace('\xa0', ' ').lower()
    # 在单词和标点符号之间插入空格
    out = [' ' + char if i > 0 and no_space(char, text[i - 1]) else char
           for i, char in enumerate(text)]
    return ''.join(out)

text = preprocess_nmt(raw_text)
print(text[:80])
go .	va !
hi .	salut !
run !	cours !
run !	courez !
who ?	qui ?
wow !	ça alors !
python 复制代码
type(text)
str
python 复制代码
#@save
def tokenize_nmt(text, num_examples=None):
    """词元化"英语-法语"数据数据集"""
    source, target = [], []
    for i, line in enumerate(text.split('\n')): # 将整个文本按换行符 \n 分割成多个句子对
        if num_examples and i > num_examples:
            break
        parts = line.split('\t') # 将每行句子对按制表符 \t 分成两个部分,即 parts[0] 为英语句子,parts[1] 为对应的法语句子
        if len(parts) == 2:
            source.append(parts[0].split(' '))
            target.append(parts[1].split(' '))
    return source, target

source, target = tokenize_nmt(text)
source[:6], target[:6]
([['go', '.'],
  ['hi', '.'],
  ['run', '!'],
  ['run', '!'],
  ['who', '?'],
  ['wow', '!']],
 [['va', '!'],
  ['salut', '!'],
  ['cours', '!'],
  ['courez', '!'],
  ['qui', '?'],
  ['ça', 'alors', '!']])
python 复制代码
#@save
def show_list_len_pair_hist(legend, xlabel, ylabel, xlist, ylist):
    """绘制列表长度对的直方图"""
    d2l.set_figsize()
    _, _, patches = d2l.plt.hist(
        [[len(l) for l in xlist], [len(l) for l in ylist]])
    d2l.plt.xlabel(xlabel)
    d2l.plt.ylabel(ylabel)
    for patch in patches[1].patches:
        patch.set_hatch('/')
    d2l.plt.legend(legend)

show_list_len_pair_hist(['source', 'target'], '# tokens per sequence',
                        'count', source, target);
python 复制代码
src_vocab = d2l.Vocab(source, min_freq=2,
                      reserved_tokens=['<pad>', '<bos>', '<eos>'])
len(src_vocab)
10012
python 复制代码
#@save
def truncate_pad(line, num_steps, padding_token):
    """截断或填充文本序列"""
    if len(line) > num_steps:
        return line[:num_steps]  # 截断
    return line + [padding_token] * (num_steps - len(line))  # 填充

truncate_pad(src_vocab[source[0]], 10, src_vocab['<pad>'])
[3919, 80, 208, 208, 208, 208, 208, 208, 208, 208]
python 复制代码
def build_array_nmt(lines, vocab, num_steps):
    """将机器翻译的文本序列转换成小批量"""
    lines = [vocab[l] for l in lines]
    lines = [l + [vocab['<eos>']] for l in lines]
    array = torch.tensor([truncate_pad(
        l, num_steps, vocab['<pad>']) for l in lines])
    valid_len = (array != vocab['<pad>']).type(torch.int32).sum(1)
    return array, valid_len
python 复制代码
def load_data_nmt(batch_size, num_steps, num_examples=600):
    """返回翻译数据集的迭代器和词表"""
    text = preprocess_nmt(read_data_nmt())
    source, target = tokenize_nmt(text, num_examples)
    src_vocab = d2l.Vocab(source, min_freq=2,
                          reserved_tokens=['<pad>', '<bos>', '<eos>'])
    tgt_vocab = d2l.Vocab(target, min_freq=2,
                          reserved_tokens=['<pad>', '<bos>', '<eos>'])
    src_array, src_valid_len = build_array_nmt(source, src_vocab, num_steps)
    tgt_array, tgt_valid_len = build_array_nmt(target, tgt_vocab, num_steps)
    data_arrays = (src_array, src_valid_len, tgt_array, tgt_valid_len)
    data_iter = d2l.load_array(data_arrays, batch_size)
    return data_iter, src_vocab, tgt_vocab
python 复制代码
train_iter, src_vocab, tgt_vocab = load_data_nmt(batch_size=2, num_steps=8)
for X, X_valid_len, Y, Y_valid_len in train_iter:
    print('X:', X.type(torch.int32))
    print('X的有效长度:', X_valid_len)
    print('Y:', Y.type(torch.int32))
    print('Y的有效长度:', Y_valid_len)
    break
X: tensor([[115, 164,   2,   4,   5,   5,   5,   5],
        [ 83,  32,   2,   4,   5,   5,   5,   5]], dtype=torch.int32)
X的有效长度: tensor([4, 4])
Y: tensor([[  6,   2,   4,   5,   5,   5,   5,   5],
        [100, 171,   6,   2,   4,   5,   5,   5]], dtype=torch.int32)
Y的有效长度: tensor([3, 5])

编码器-解码器

python 复制代码
from torch import nn


#@save
class Encoder(nn.Module):
    """编码器-解码器架构的基本编码器接口"""
    def __init__(self, **kwargs):
        super(Encoder, self).__init__(**kwargs)

    def forward(self, X, *args):
        raise NotImplementedError
python 复制代码
#@save
class Decoder(nn.Module):
    """编码器-解码器架构的基本解码器接口"""
    def __init__(self, **kwargs):
        super(Decoder, self).__init__(**kwargs)

    def init_state(self, enc_outputs, *args):
        raise NotImplementedError

    def forward(self, X, state):
        raise NotImplementedError
python 复制代码
#@save
class EncoderDecoder(nn.Module):
    """编码器-解码器架构的基类"""
    def __init__(self, encoder, decoder, **kwargs):
        super(EncoderDecoder, self).__init__(**kwargs)
        self.encoder = encoder
        self.decoder = decoder

    def forward(self, enc_X, dec_X, *args):
        enc_outputs = self.encoder(enc_X, *args)
        dec_state = self.decoder.init_state(enc_outputs, *args)
        return self.decoder(dec_X, dec_state)

序列到序列的学习

python 复制代码
import collections
import math
import torch
from torch import nn
from d2l import torch as d2l
python 复制代码
#@save
class Seq2SeqEncoder(d2l.Encoder):
    """用于序列到序列学习的循环神经网络编码器"""
    def __init__(self, vocab_size, embed_size, num_hiddens, num_layers,
                 dropout=0, **kwargs):
        super(Seq2SeqEncoder, self).__init__(**kwargs)
        # 嵌入层
        self.embedding = nn.Embedding(vocab_size, embed_size)
        self.rnn = nn.GRU(embed_size, num_hiddens, num_layers, dropout=dropout)

    def forward(self, X, *args):
        # 输出'X'的形状:(batch_size,num_steps,embed_size)
        X = self.embedding(X)
        # 在循环神经网络模型中,第一个轴对应于时间步
        X = X.permute(1, 0, 2)
        # 如果未提及状态,则默认为0
        output, state = self.rnn(X)
        # output的形状:(num_steps,batch_size,num_hiddens)
        # state的形状:(num_layers * num_directions,batch_size,num_hiddens)
        return output, state
python 复制代码
encoder = Seq2SeqEncoder(vocab_size=10, embed_size=8, num_hiddens=16,
                         num_layers=2)
encoder.eval()
X = torch.zeros((4, 7), dtype=torch.long)
output, state = encoder(X)
output.shape
torch.Size([7, 4, 16])
python 复制代码
state.shape
torch.Size([2, 4, 16])
python 复制代码
class Seq2SeqDecoder(d2l.Decoder):
    """用于序列到序列学习的循环神经网络解码器"""
    def __init__(self, vocab_size, embed_size, num_hiddens, num_layers,
                 dropout=0, **kwargs):
        super(Seq2SeqDecoder, self).__init__(**kwargs)
        self.embedding = nn.Embedding(vocab_size, embed_size)
        self.rnn = nn.GRU(embed_size + num_hiddens, num_hiddens, num_layers,
                          dropout=dropout)
        self.dense = nn.Linear(num_hiddens, vocab_size)

    def init_state(self, enc_outputs, *args):
        return enc_outputs[1]

    def forward(self, X, state):
        # 输出'X'的形状:(batch_size,num_steps,embed_size)
        X = self.embedding(X).permute(1, 0, 2)
        # 广播context,使其具有与X相同的num_steps
        context = state[-1].repeat(X.shape[0], 1, 1) # 使得其可以与 X 在时间步维度上拼接,使得每个时间步的输入都包含上下文信息
        X_and_context = torch.cat((X, context), 2)
        output, state = self.rnn(X_and_context, state)
        output = self.dense(output).permute(1, 0, 2)
        # output的形状:(batch_size,num_steps,vocab_size)
        # state的形状:(num_layers * n_derection,batch_size,num_hiddens)
        return output, state
python 复制代码
decoder = Seq2SeqDecoder(vocab_size=10, embed_size=8, num_hiddens=16,
                         num_layers=2)
decoder.eval()
state = decoder.init_state(encoder(X))
output, state = decoder(X, state)
output.shape, state.shape
(torch.Size([4, 7, 10]), torch.Size([2, 4, 16]))
python 复制代码
#@save
def sequence_mask(X, valid_len, value=0):
    """在序列中屏蔽不相关的项"""
    maxlen = X.size(1)
#     print(torch.arange((maxlen), dtype=torch.float32, device=X.device)[None, :]< valid_len[:, None])
    mask = torch.arange((maxlen), dtype=torch.float32,
                        device=X.device)[None, :] < valid_len[:, None]
    X[~mask] = value
    return X

X = torch.tensor([[1, 2, 3], [4, 5, 6]])
sequence_mask(X, torch.tensor([1, 2]))
tensor([[1, 0, 0],
        [4, 5, 0]])
python 复制代码
X = torch.ones(2, 3, 4)
sequence_mask(X, torch.tensor([1, 2]), value=-1)
tensor([[[ 1.,  1.,  1.,  1.],
         [-1., -1., -1., -1.],
         [-1., -1., -1., -1.]],

        [[ 1.,  1.,  1.,  1.],
         [ 1.,  1.,  1.,  1.],
         [-1., -1., -1., -1.]]])
python 复制代码
#@save
class MaskedSoftmaxCELoss(nn.CrossEntropyLoss):
    """带遮蔽的softmax交叉熵损失函数"""
    # pred的形状:(batch_size,num_steps,vocab_size)
    # label的形状:(batch_size,num_steps)
    # valid_len的形状:(batch_size,)
    def forward(self, pred, label, valid_len):
        weights = torch.ones_like(label)
        weights = sequence_mask(weights, valid_len)
        self.reduction='none'
        unweighted_loss = super(MaskedSoftmaxCELoss, self).forward(
            pred.permute(0, 2, 1), label) # nn.CrossEntropyLoss 期望输入 pred 的形状为 (batch_size, vocab_size, num_steps),因此需要对 pred 进行转置操作 pred.permute(0, 2, 1) 以匹配这种形状。
        weighted_loss = (unweighted_loss * weights).mean(dim=1)
        return weighted_loss
python 复制代码
loss = MaskedSoftmaxCELoss()
loss(torch.ones(3, 4, 10), torch.ones((3, 4), dtype=torch.long),
     torch.tensor([4, 2, 0]))
tensor([2.3026, 1.1513, 0.0000])
python 复制代码
#@save
def train_seq2seq(net, data_iter, lr, num_epochs, tgt_vocab, device):
    """训练序列到序列模型"""
    def xavier_init_weights(m):
        if type(m) == nn.Linear:
            nn.init.xavier_uniform_(m.weight)
        if type(m) == nn.GRU:
            for param in m._flat_weights_names:
                if "weight" in param:
                    nn.init.xavier_uniform_(m._parameters[param])

    net.apply(xavier_init_weights)
    net.to(device)
    optimizer = torch.optim.Adam(net.parameters(), lr=lr)
    loss = MaskedSoftmaxCELoss()
    net.train()
    animator = d2l.Animator(xlabel='epoch', ylabel='loss',
                     xlim=[10, num_epochs])
    for epoch in range(num_epochs):
        timer = d2l.Timer()
        metric = d2l.Accumulator(2)  # 训练损失总和,词元数量
        for batch in data_iter:
            optimizer.zero_grad()
            X, X_valid_len, Y, Y_valid_len = [x.to(device) for x in batch]
            bos = torch.tensor([tgt_vocab['<bos>']] * Y.shape[0],
                          device=device).reshape(-1, 1)
            dec_input = torch.cat([bos, Y[:, :-1]], 1)  # 强制教学
            Y_hat, _ = net(X, dec_input, X_valid_len)
            l = loss(Y_hat, Y, Y_valid_len)
            l.sum().backward()      # 损失函数的标量进行"反向传播"
            d2l.grad_clipping(net, 1)
            num_tokens = Y_valid_len.sum()
            optimizer.step()
            with torch.no_grad():
                metric.add(l.sum(), num_tokens)
        if (epoch + 1) % 10 == 0:
            animator.add(epoch + 1, (metric[0] / metric[1],))
    print(f'loss {metric[0] / metric[1]:.3f}, {metric[1] / timer.stop():.1f} '
        f'tokens/sec on {str(device)}')
python 复制代码
embed_size, num_hiddens, num_layers, dropout = 32, 32, 2, 0.1
batch_size, num_steps = 64, 10
lr, num_epochs, device = 0.005, 200, d2l.try_gpu()

train_iter, src_vocab, tgt_vocab = d2l.load_data_nmt(batch_size, num_steps)
encoder = Seq2SeqEncoder(len(src_vocab), embed_size, num_hiddens, num_layers,
                        dropout)
decoder = Seq2SeqDecoder(len(tgt_vocab), embed_size, num_hiddens, num_layers,
                        dropout)
net = EncoderDecoder(encoder, decoder) # 不要加d2l,否则报错
train_seq2seq(net, train_iter, lr, num_epochs, tgt_vocab, device)
loss 0.020, 11904.7 tokens/sec on cuda:0
python 复制代码
#@save
def predict_seq2seq(net, src_sentence, src_vocab, tgt_vocab, num_steps,
                    device, save_attention_weights=False):
    """序列到序列模型的预测"""
    # 在预测时将net设置为评估模式
    net.eval()
    src_tokens = src_vocab[src_sentence.lower().split(' ')] + [
        src_vocab['<eos>']]
    enc_valid_len = torch.tensor([len(src_tokens)], device=device)
    src_tokens = d2l.truncate_pad(src_tokens, num_steps, src_vocab['<pad>'])
    # 添加批量轴
    enc_X = torch.unsqueeze(
        torch.tensor(src_tokens, dtype=torch.long, device=device), dim=0)
    enc_outputs = net.encoder(enc_X, enc_valid_len)
    dec_state = net.decoder.init_state(enc_outputs, enc_valid_len)
    # 添加批量轴
    dec_X = torch.unsqueeze(torch.tensor(
        [tgt_vocab['<bos>']], dtype=torch.long, device=device), dim=0)
    output_seq, attention_weight_seq = [], []
    for _ in range(num_steps):
        Y, dec_state = net.decoder(dec_X, dec_state)
        # 我们使用具有预测最高可能性的词元,作为解码器在下一时间步的输入
        dec_X = Y.argmax(dim=2)
        pred = dec_X.squeeze(dim=0).type(torch.int32).item()
        # 保存注意力权重(稍后讨论)
        if save_attention_weights:
            attention_weight_seq.append(net.decoder.attention_weights)
        # 一旦序列结束词元被预测,输出序列的生成就完成了
        if pred == tgt_vocab['<eos>']:
            break
        output_seq.append(pred)
    return ' '.join(tgt_vocab.to_tokens(output_seq)), attention_weight_seq
python 复制代码
def bleu(pred_seq, label_seq, k):  #@save
    """计算BLEU"""
    pred_tokens, label_tokens = pred_seq.split(' '), label_seq.split(' ')
    len_pred, len_label = len(pred_tokens), len(label_tokens)
    score = math.exp(min(0, 1 - len_label / len_pred))
    for n in range(1, k + 1):
        num_matches, label_subs = 0, collections.defaultdict(int)
        for i in range(len_label - n + 1):
            label_subs[' '.join(label_tokens[i: i + n])] += 1
        for i in range(len_pred - n + 1):
            if label_subs[' '.join(pred_tokens[i: i + n])] > 0:
                num_matches += 1
                label_subs[' '.join(pred_tokens[i: i + n])] -= 1
        score *= math.pow(num_matches / (len_pred - n + 1), math.pow(0.5, n))
    return score
python 复制代码
engs = ['go .', "i lost .", 'he\'s calm .', 'i\'m home .']
fras = ['va !', 'j\'ai perdu .', 'il est calme .', 'je suis chez moi .']
for eng, fra in zip(engs, fras):
    translation, attention_weight_seq = predict_seq2seq(
        net, eng, src_vocab, tgt_vocab, num_steps, device)
    print(f'{eng} => {translation}, bleu {bleu(translation, fra, k=2):.3f}')
go . => va !, bleu 1.000
i lost . => j'ai perdu ., bleu 1.000
he's calm . => il est mouillé paresseux ., bleu 0.548
i'm home . => je suis chez juste !, bleu 0.651

代码来自:https://zh.d2l.ai/chapter_recurrent-neural-networks/sequence.html

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