%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 = d2l.load_data_time_machine(batch_size, num_steps)
独热编码
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]])
小批量形状是(批量大小, 时间步数)
X = torch.arange(10).reshape((2, 5))
F.one_hot(X.T, 28).shape
torch.Size([5, 2, 28])
初始化循环神经网络模型的模型参数
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
W_xh = normal((num_inputs, num_hiddens))
W_hh = normal((num_hiddens, num_hiddens))
b_h = torch.zeros(num_hiddens, device=device)
W_hq = normal((num_hiddens, num_outputs))
b_q = torch.zeros(num_outputs, device=device)
params = [W_xh, W_hh, b_h, W_hq, b_q]
for param in params:
param.requires_grad_(True)
return params
一个init_rnn_state函数在初始化时返回隐藏状态
def init_rnn_state(batch_size, num_hiddens, device):
return (torch.zeros((batch_size, num_hiddens), device=device),)
下面的rnn函数定义了如何在一个时间步计算隐藏状态和输出
def rnn(inputs, state, params):
W_xh, W_hh, b_h, W_hq, b_q = params
H, = state
outputs = []
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,)
创建一个类来包装这些函数
class RNNModelScratch:
"""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)
检查输出是否具有正确的形状
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]))
首先定义预测函数来生成用户提供的prefix之后的新字符
def predict_ch8(prefix, num_preds, net, vocab, device):
"""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:]:
_, state = net(get_input(), state)
outputs.append(vocab[y])
for _ in range(num_preds):
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])
predict_ch8('time traveller ', 10, net, vocab, d2l.try_gpu())
'time traveller fnhghghghg'
梯度裁剪 $$\mathbf{g} \leftarrow \min\left(1, \frac{\theta}{\|\mathbf{g}\|}\right) \mathbf{g}$$
def grad_clipping(net, theta):
"""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
定义一个函数来训练只有一个迭代周期的模型
def train_epoch_ch8(net, train_iter, loss, updater, device, use_random_iter):
"""训练模型一个迭代周期（定义见第8章）。"""
state, timer = None, d2l.Timer()
metric = d2l.Accumulator(2)
for X, Y in train_iter:
if state is None or use_random_iter:
state = net.begin_state(batch_size=X.shape[0], device=device)
else:
if isinstance(net, nn.Module) and not isinstance(state, tuple):
state.detach_()
else:
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)
updater(batch_size=1)
metric.add(l * y.numel(), y.numel())
return math.exp(metric[0] / metric[1]), metric[1] / timer.stop()
训练函数支持从零开始或使用高级API实现的循环神经网络模型
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])
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)
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} 标记/秒 {str(device)}')
print(predict('time traveller'))
print(predict('traveller'))
现在我们可以训练循环神经网络模型
num_epochs, lr = 500, 1
train_ch8(net, train_iter, vocab, lr, num_epochs, d2l.try_gpu())
困惑度 1.0, 62622.4 标记/秒 cuda:0 time travelleryou can show black is white by argument said filby travelleryou can show black is white by argument said filby
最后，让我们检查一下使用随机抽样方法的结果
train_ch8(net, train_iter, vocab, lr, num_epochs, d2l.try_gpu(),
use_random_iter=True)
困惑度 1.4, 62407.4 标记/秒 cuda:0 time travellerit s against reason said filbywhat we convenient t travellerit s against reason said filbywhat we convenient t