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Fendy
2026-07-16 14:39:39 +08:00
parent 836060ecdf
commit e9d9d5a2af
2 changed files with 140 additions and 44 deletions
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transformer.py
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@@ -2,155 +2,237 @@ import numpy as np
def softmax(x, axis=-1):
"""Softmax激活函数，用于将 logits 转换为概率分布"""
# 减去最大值防止数值溢出
e_x = np.exp(x - np.max(x, axis=axis, keepdims=True))
return e_x / np.sum(e_x, axis=axis, keepdims=True)
def relu(x):
"""ReLU激活函数"""
return np.maximum(0, x)
class Linear:
"""全连接层（线性层）"""
def __init__(self, in_features, out_features):
# 使用He初始化权重
self.weight = np.random.randn(in_features, out_features) * np.sqrt(2.0 / in_features)
# 偏置初始化为0
self.bias = np.zeros(out_features)
def forward(self, x):
"""前向传播：y = xW + b"""
return x @ self.weight + self.bias
class LayerNorm:
"""层归一化（Layer Normalization）"""
def __init__(self, d_model, eps=1e-6):
# 缩放参数
self.gamma = np.ones(d_model)
# 偏移参数
self.beta = np.zeros(d_model)
# 防止除零的小常数
self.eps = eps
def forward(self, x):
"""前向传播：对最后一个维度进行归一化"""
mean = np.mean(x, axis=-1, keepdims=True)
std = np.std(x, axis=-1, keepdims=True)
return self.gamma * (x - mean) / (std + self.eps) + self.beta
class MultiHeadAttention:
"""多头注意力机制"""
def __init__(self, d_model, num_heads):
self.d_model = d_model
self.num_heads = num_heads
self.d_k = d_model // num_heads
self.d_model = d_model # 模型维度
self.num_heads = num_heads # 注意力头数
self.d_k = d_model // num_heads # 每个头的维度
self.W_q = Linear(d_model, d_model)
self.W_k = Linear(d_model, d_model)
self.W_v = Linear(d_model, d_model)
self.W_o = Linear(d_model, d_model)
# 定义Q、K、V的线性变换层
self.W_q = Linear(d_model, d_model) # Query变换
self.W_k = Linear(d_model, d_model) # Key变换
self.W_v = Linear(d_model, d_model) # Value变换
self.W_o = Linear(d_model, d_model) # 输出变换
def forward(self, Q, K, V, mask=None):
"""
前向传播
Q: Query张量 [batch_size, seq_len, d_model]
K: Key张量 [batch_size, seq_len, d_model]
V: Value张量 [batch_size, seq_len, d_model]
mask: 注意力掩码
"""
batch_size = Q.shape[0]
seq_len = Q.shape[1]
# 线性变换并分割成多头
Q = self.W_q.forward(Q).reshape(batch_size, seq_len, self.num_heads, self.d_k).transpose(0, 2, 1, 3)
K = self.W_k.forward(K).reshape(batch_size, seq_len, self.num_heads, self.d_k).transpose(0, 2, 1, 3)
V = self.W_v.forward(V).reshape(batch_size, seq_len, self.num_heads, self.d_k).transpose(0, 2, 1, 3)
# 计算缩放点积注意力分数
attn_scores = Q @ K.transpose(0, 1, 3, 2) / np.sqrt(self.d_k)
# 应用掩码（如果提供）
if mask is not None:
attn_scores = np.where(mask == 0, -1e9, attn_scores)
# Softmax得到注意力权重
attn_probs = softmax(attn_scores, axis=-1)
# 加权求和
attn_output = attn_probs @ V
# 拼接多头输出
attn_output = attn_output.transpose(0, 2, 1, 3).reshape(batch_size, seq_len, self.d_model)
# 最终线性变换
output = self.W_o.forward(attn_output)
return output
class FeedForward:
"""前馈神经网络（两层全连接网络）"""
def __init__(self, d_model, d_ff):
# 第一层：扩展维度
self.linear1 = Linear(d_model, d_ff)
# 第二层：恢复维度
self.linear2 = Linear(d_ff, d_model)
def forward(self, x):
"""前向传播：线性 -> ReLU -> 线性"""
return self.linear2.forward(relu(self.linear1.forward(x)))
class TransformerBlock:
"""Transformer编码器块"""
def __init__(self, d_model, num_heads, d_ff):
# 多头自注意力层
self.attention = MultiHeadAttention(d_model, num_heads)
# 前馈网络层
self.feed_forward = FeedForward(d_model, d_ff)
# 两个层归一化
self.norm1 = LayerNorm(d_model)
self.norm2 = LayerNorm(d_model)
def forward(self, x, mask=None):
"""
前向传播（残差连接 + 层归一化）
1. 自注意力 -> 残差连接 -> 层归一化
2. 前馈网络 -> 残差连接 -> 层归一化
"""
# 自注意力子层
attn_output = self.attention.forward(x, x, x, mask)
x = self.norm1.forward(x + attn_output)
# 前馈网络子层
ff_output = self.feed_forward.forward(x)
x = self.norm2.forward(x + ff_output)
return x
class SimpleTransformer:
"""简化的Transformer编码器模型"""
def __init__(self, vocab_size, d_model, num_heads, num_layers, d_ff, max_seq_len):
self.d_model = d_model
# 词嵌入层
self.embedding = np.random.randn(vocab_size, d_model) * 0.01
# 位置编码
self.positional_encoding = self._create_positional_encoding(max_seq_len, d_model)
# Transformer编码器层堆叠
self.transformer_blocks = [
TransformerBlock(d_model, num_heads, d_ff) for _ in range(num_layers)
]
def _create_positional_encoding(self, max_seq_len, d_model):
"""
创建正弦余弦位置编码
使用不同频率的正弦和余弦函数生成位置信息
"""
pe = np.zeros((max_seq_len, d_model))
position = np.arange(0, max_seq_len).reshape(-1, 1).astype(float)
div_term = np.exp(np.arange(0, d_model, 2).astype(float) * -(np.log(10000.0) / d_model))
pe[:, 0::2] = np.sin(position * div_term)
pe[:, 1::2] = np.cos(position * div_term)
pe[:, 0::2] = np.sin(position * div_term) # 偶数维度用正弦
pe[:, 1::2] = np.cos(position * div_term) # 奇数维度用余弦
return pe
def forward(self, x, mask=None):
"""
前向传播
x: 输入序列 [batch_size, seq_len]
mask: 注意力掩码
"""
seq_len = x.shape[1]
# 词嵌入 + 缩放
x = self.embedding[x] * np.sqrt(self.d_model)
# 加上位置编码
x = x + self.positional_encoding[:seq_len, :]
# 通过所有Transformer块
for block in self.transformer_blocks:
x = block.forward(x, mask)
return x
def count_parameters(self):
"""统计模型参数数量"""
count = 0
count += self.embedding.size
count += self.embedding.size # 嵌入层参数
for block in self.transformer_blocks:
# 注意力层参数
count += block.attention.W_q.weight.size + block.attention.W_q.bias.size
count += block.attention.W_k.weight.size + block.attention.W_k.bias.size
count += block.attention.W_v.weight.size + block.attention.W_v.bias.size
count += block.attention.W_o.weight.size + block.attention.W_o.bias.size
# 前馈网络参数
count += block.feed_forward.linear1.weight.size + block.feed_forward.linear1.bias.size
count += block.feed_forward.linear2.weight.size + block.feed_forward.linear2.bias.size
# 层归一化参数
count += block.norm1.gamma.size + block.norm1.beta.size
count += block.norm2.gamma.size + block.norm2.beta.size
return count
def create_padding_mask(seq, pad_idx=0):
"""
创建填充掩码
用于忽略序列中的填充位置（padding tokens）
"""
return (seq != pad_idx).astype(float)[:, np.newaxis, np.newaxis, :]
def create_look_ahead_mask(size):
"""
创建前瞻掩码（下三角掩码）
用于解码器中，防止位置i看到i之后的信息
"""
mask = np.triu(np.ones((size, size)), k=1).astype(bool)
return (~mask).astype(float)
if __name__ == "__main__":
vocab_size = 1000
d_model = 512
num_heads = 8
num_layers = 6
d_ff = 2048
max_seq_len = 100
# 模型超参数
vocab_size = 1000 # 词汇表大小
d_model = 512 # 模型维度
num_heads = 8 # 注意力头数
num_layers = 6 # Transformer层数
d_ff = 2048 # 前馈网络隐藏层维度
max_seq_len = 100 # 最大序列长度
# 创建模型
model = SimpleTransformer(vocab_size, d_model, num_heads, num_layers, d_ff, max_seq_len)
# 创建随机输入
batch_size = 2
seq_len = 10
x = np.random.randint(0, vocab_size, (batch_size, seq_len))
# 前向传播
output = model.forward(x)
print(f"Input shape: {x.shape}")
print(f"Output shape: {output.shape}")
print(f"Model parameters: {model.count_parameters():,}")
print(f"输入形状: {x.shape}")
print(f"输出形状: {output.shape}")
print(f"模型参数量: {model.count_parameters():,}")