神经网络常见层Numpy封装参考（5）：其他层

目录

• 前置层
• 其他层
• • BatchNorm1d层
  • • 封装
    • 测试
  • BatchNorm2d层
  • • 封装
  • Dropout层
  • • 封装
    • 测试

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完整代码下载 ：神经网络常见层Numpy封装参考 - 常见层

前置层

- 神经网络常见层Numpy封装参考（1）：损失层
- 神经网络常见层Numpy封装参考（2）：线性层
- 神经网络常见层Numpy封装参考（3）：激活层
- 神经网络常见层Numpy封装参考（4）：优化器

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其他层

BatchNorm1d层

输入数据
X ( N × C ) = x 1 ( 1 ) x 1 ( 2 ) ⋯ x 1 ( C ) x 2 ( 1 ) x 2 ( 2 ) ⋯ x 2 ( C ) ⋯ ⋯ ⋯ ⋯ x N ( 1 ) x N ( 2 ) ⋯ x N ( C ) {{\bf{X}}_{(N \times C)}} = \left {\\begin{array}{c} {{x_1}\^{(1)}}\&{{x_1}\^{(2)}}\& \\cdots \&{{x_1}\^{(C)}}\\\\ {{x_2}\^{(1)}}\&{{x_2}\^{(2)}}\& \\cdots \&{{x_2}\^{(C)}}\\\\ \\cdots \& \\cdots \& \\cdots \& \\cdots \\\\ {{x_N}\^{(1)}}\&{{x_N}\^{(2)}}\& \\cdots \&{{x_N}\^{(C)}} \\end{array}} \\right X(N×C)= x1(1)x2(1)⋯xN(1)x1(2)x2(2)⋯xN(2)⋯⋯⋯⋯x1(C)x2(C)⋯xN(C)

从批次维度计算得到的均值和方差向量
μ ( 1 × C ) = ( X ^ ( N × C ) ) . m e a n ( a x i s = 0 ) v a r ( 1 × C ) = ( X ^ ( N × C ) ) . v a r ( a x i s = 0 ) \begin{array}{l} {{\bf{\mu }}{(1 \times C)}} = \left( {{{{\bf{\hat X}}}{(N \times C)}}} \right){\rm{.mean(axis = 0)}}\\ {\bf{va}}{{\bf{r}}{(1 \times C)}} = \left( {{{{\bf{\hat X}}}{(N \times C)}}} \right){\rm{.var(axis = 0)}} \end{array} μ(1×C)=(X^(N×C)).mean(axis=0)var(1×C)=(X^(N×C)).var(axis=0)

缩放与偏移学习参数，目标是寻找使损失最小化的最优数据分布均值和方差
γ ( 1 × C ) = γ ( 1 ) γ ( 2 ) ⋯ γ ( C ) β ( 1 × C ) = β ( 1 ) β ( 2 ) ⋯ β ( C ) \begin{array}{l} {{\bf{\gamma }}{(1 \times C)}} = \left {\\begin{array}{c} {{\\gamma \^{(1)}}}\&{{\\gamma \^{(2)}}}\& \\cdots \&{{\\gamma \^{(C)}}} \\end{array}} \\right\\ {{\bf{\beta }}{(1 \times C)}} = \left {\\begin{array}{c} {{\\beta \^{(1)}}}\&{{\\beta \^{(2)}}}\& \\cdots \&{{\\beta \^{(C)}}} \\end{array}} \\right \end{array} γ(1×C)=γ(1)γ(2)⋯γ(C)β(1×C)=β(1)β(2)⋯β(C)

训练模式前向传播
Y ( N × C ) = γ ( 1 × C ) × X ( N × C ) − μ ( 1 × C ) v a r ( 1 × C ) + ε + β ( 1 × C ) {{\bf{Y}}{(N \times C)}} = {{\bf{\gamma }}{(1 \times C)}} \times \frac{{{{\bf{X}}{(N \times C)}} - {{\bf{\mu }}{(1 \times C)}}}}{{\sqrt {{\bf{va}}{{\bf{r}}{(1 \times C)}} + \varepsilon } }} + {{\bf{\beta }}{(1 \times C)}} Y(N×C)=γ(1×C)×var(1×C)+ε X(N×C)−μ(1×C)+β(1×C)

评估模式前向传播
μ r u n i n g ( 1 × C ) ← ( 1 − m o m e n t u m ) × μ r u n i n g ( 1 × C ) + m o m e n t u m × μ ( 1 × C ) v a r r u n i n g ( 1 × C ) ← ( 1 − m o m e n t u m ) × v a r r u n i n g ( 1 × C ) + m o m e n t u m × v a r ( 1 × C ) Y ( N × C ) = γ ( 1 × C ) × X ( N × C ) − μ r u n i n g ( 1 × C ) v a r r u n i n g ( 1 × C ) + ε + β ( 1 × C ) \begin{array}{l} \mathop {{{\bf{\mu }}{{\rm{runing}}}}}\limits^{(1 \times C)} \leftarrow \left( {1 - {\rm{momentum}}} \right) \times \mathop {{{\bf{\mu }}{{\rm{runing}}}}}\limits^{(1 \times C)} + {\rm{momentum}} \times {{\bf{\mu }}{(1 \times C)}}\\ \mathop {{\bf{va}}{{\bf{r}}{{\rm{runing}}}}}\limits^{(1 \times C)} \leftarrow \left( {1 - {\rm{momentum}}} \right) \times \mathop {{\bf{va}}{{\bf{r}}{{\rm{runing}}}}}\limits^{(1 \times C)} + {\rm{momentum}} \times {\bf{va}}{{\bf{r}}{(1 \times C)}}\\ {{\bf{Y}}{(N \times C)}} = {{\bf{\gamma }}{(1 \times C)}} \times \frac{{{{\bf{X}}{(N \times C)}} - \mathop {{{\bf{\mu }}{{\rm{runing}}}}}\limits^{(1 \times C)} }}{{\sqrt {\mathop {{\bf{va}}{{\bf{r}}{{\rm{runing}}}}}\limits^{(1 \times C)} + \varepsilon } }} + {{\bf{\beta }}{(1 \times C)}} \end{array} μruning(1×C)←(1−momentum)×μruning(1×C)+momentum×μ(1×C)varruning(1×C)←(1−momentum)×varruning(1×C)+momentum×var(1×C)Y(N×C)=γ(1×C)×varruning(1×C)+ε X(N×C)−μruning(1×C)+β(1×C)

层梯度
G R A D ( N × C ) = γ ( 1 × C ) v a r ( 1 × C ) + ε × ( g r a d ( N × C ) − 1 N ⋅ g r a d . s u m ( a x i s = 0 ) ( 1 × C ) − 1 N ⋅ X ^ ( N × C ) × ( g r a d ( N × C ) × X ^ ( N × C ) ) . s u m ( a x i s = 0 ) ( 1 × C ) ) {\bf{GRA}}{{\bf{D}}{(N \times C)}} = \frac{{{{\bf{\gamma }}{(1 \times C)}}}}{{\sqrt {{\bf{va}}{{\bf{r}}{(1 \times C)}} + \varepsilon } }} \times \left( {{\bf{gra}}{{\bf{d}}{(N \times C)}} - \frac{1}{N} \cdot \mathop {{\bf{grad}}{\rm{.sum(axis = 0)}}}\limits^{(1 \times C)} - \frac{1}{N} \cdot {{{\bf{\hat X}}}{(N \times C)}} \times \left( {{\bf{gra}}{{\bf{d}}{(N \times C)}} \times {{{\bf{\hat X}}}_{(N \times C)}}} \right)\mathop {{\rm{.sum(axis = 0)}}}\limits^{(1 \times C)} } \right) GRAD(N×C)=var(1×C)+ε γ(1×C)×(grad(N×C)−N1⋅grad.sum(axis=0)(1×C)−N1⋅X^(N×C)×(grad(N×C)×X^(N×C)).sum(axis=0)(1×C))

可学习参数梯度
d γ ( 1 × C ) = ( g r a d ( N × C ) × X n o r m ( N × C ) ) . s u m ( a x i s = 0 ) d β ( 1 × C ) = ( g r a d ( N × C ) ) . s u m ( a x i s = 0 ) \begin{array}{l} {\bf{d}}{{\bf{\gamma }}{(1 \times C)}} = \left( {{\bf{gra}}{{\bf{d}}{(N \times C)}} \times \mathop {{{\bf{X}}{{\bf{norm}}}}}\limits^{(N \times C)} } \right).sum(axis = 0)\\ {\bf{d}}{{\bf{\beta }}{(1 \times C)}} = \left( {{\bf{gra}}{{\bf{d}}_{(N \times C)}}} \right){\rm{.sum(axis = 0)}} \end{array} dγ(1×C)=(grad(N×C)×Xnorm(N×C)).sum(axis=0)dβ(1×C)=(grad(N×C)).sum(axis=0)

推导过程参考：神经网络批归一化层梯度公式推导

封装

class BatchNorm1d(Module):
    def __init__(self, num_features, eps=1e-5, momentum=0.1):
        """
        参数:
            num_features: 输入特征的数量 (C)
            eps: 数值稳定性常数
            momentum: 移动平均的动量
        """
        super().__init__()
        
        self.eps = eps
        self.momentum = momentum
        self.num_features = num_features
        
        # 可训练参数（需要更新）
        self.gamma = Parameter(np.ones((1, num_features)), requires_grad=True)      # 缩放参数
        self.beta = Parameter(np.zeros((1, num_features)), requires_grad=True)       # 平移参数
        
        # 移动平均参数（评估时使用）
        self.running_mean = np.zeros((1, num_features))
        self.running_var = np.ones((1, num_features))
        
        # 缓存中间变量（用于反向传播）
        self.cache = {}
        
    def forward(self, x):
        """
        Args:
            x: 输入数据，形状可以是 (N, C) 或 (N, C, L)

        """
        # 保存输入形状，用于恢复
        input_shape = x.shape
        
        # 处理不同维度的输入
        if len(input_shape) == 3:  # (N, C, L)
            N, C, L = input_shape
            # 重排为 (N*L, C) 方便计算
            x = x.transpose(0, 2, 1).reshape(-1, C)
            self.cache['input_shape'] = input_shape
            self.cache['N'] = N
            self.cache['C'] = C
            self.cache['L'] = L
        else:  # (N, C)
            N, C = input_shape
            self.cache['input_shape'] = input_shape
            self.cache['N'] = N
            self.cache['C'] = C
            self.cache['L'] = 1
        
        if self.training:
            # 计算当前批次的均值和方差
            batch_mean = np.mean(x, axis=0, keepdims=True)
            batch_var = np.var(x, axis=0, keepdims=True)
            
            # 更新移动平均
            self.running_mean = (1 - self.momentum) * self.running_mean + self.momentum * batch_mean
            self.running_var = (1 - self.momentum) * self.running_var + self.momentum * batch_var
            
            # 归一化
            x_norm = (x - batch_mean) / np.sqrt(batch_var + self.eps)
            
            # 缓存中间变量用于反向传播
            self.cache['batch_mean'] = batch_mean
            self.cache['batch_var'] = batch_var
            self.cache['x_norm'] = x_norm
        else:
            # 评估模式：使用移动平均
            x_norm = (x - self.running_mean) / np.sqrt(self.running_var + self.eps)
        
        # 缩放和平移
        out = self.gamma.data * x_norm + self.beta.data
        self.cache['out'] = out
        
        # 恢复原始形状
        if (len(input_shape) == 3):
            out = out.reshape(N, L, C).transpose(0, 2, 1)
        
        return out
    
    def backward(self, grad):
        # 处理不同维度的输入
        if len(self.cache['input_shape']) == 3:
            N, C, L = self.cache['input_shape']
            # 将梯度重排为 (N*L, C)
            grad = grad.transpose(0, 2, 1).reshape(-1, C)
        else:
            N, C = self.cache['input_shape']
        
        # 获取缓存的中间变量
        batch_mean = self.cache['batch_mean']
        batch_var = self.cache['batch_var']
        x_norm = self.cache['x_norm']
        
        # 计算 gamma 和 beta 的梯度
        self.gamma.grad += np.sum(grad * x_norm, axis=0, keepdims=True)
        self.beta.grad += np.sum(grad, axis=0, keepdims=True)
        
        # 层梯度
        dx = self.gamma.data / np.sqrt(batch_var + self.eps) * (grad - grad.sum(axis=0, keepdims=True) / N - x_norm * (grad * x_norm).sum(axis=0, keepdims=True) / N)
        
        # 恢复原始形状
        if len(self.cache['input_shape']) == 3:
            dx = dx.reshape(N, L, C).transpose(0, 2, 1)
        
        return dx
    
    def __call__(self, x):
        return self.forward(x)

    def __repr__(self):
        return self.__class__.__name__ + f'(num_features={self.num_features}, eps={self.eps}, momentum={self.momentum})'

测试

%matplotlib inline

# 数据点满足非线性关系
x = np.linspace(0, 1, 500).reshape(-1, 1)
y = 2 * x**3 + 0.2* np.random.randn(500).reshape(-1, 1)

plt.scatter(x, y)
plt.show()

​

​

# 定义模型和损失函数
model = Sequential(
    Linear(1, 15),
    Tanh(),
    BatchNorm1d(15),
    Linear(15, 1),
)
criterion = MSELoss()

optimizer = Adam(params=model.parameters(), lr=1e-2)

model.train()
# 训练流程
for epoch in range(200):
    y_pred = model(x)
    loss, grad = criterion(y_pred, y)
    model.backward(grad)
    optimizer.step()
    optimizer.zero_grad()

    if(epoch % 200 == 0):
        print(loss)

0.6625318142073177

%matplotlib inline

model.eval()
# 检验拟合效果
x_plot = np.linspace(0, 1.2, 50).reshape(-1, 1)
plt.plot(x_plot, model(x_plot), c='r')
plt.scatter(x, y)
plt.show()

​

---

BatchNorm2d层

如果输入数据为批处理图像，即具有 N × C × H × W N \times C \times H \times W N×C×H×W形状的数据，那么只需将最后两个维度展平，然后传入BatchNorm1d层处理即可。

封装

class BatchNorm2d(BatchNorm1d):
    def __init__(self, num_features, eps=1e-5, momentum=0.1):
        """
        参数:
            num_features: 输入特征的数量 (C)
            eps: 数值稳定性常数
            momentum: 移动平均的动量
        """
        super().__init__(num_features, eps, momentum)
        
        self.input_shape = None
        
    def forward(self, x):
        """
        Args:
            x: 输入数据，形状为 (N, C, H, W) 

        """
        # 保存输入形状，用于恢复
        self.input_shape = x.shape

        # 四个维度分别为批次数、通道数、图像高度、图像宽度
        N, C, H, W = self.input_shape
        # 展平后两个维度
        x = x.reshape(N, C, H*W)
        # 传入父类前向传播
        out = super().forward(x)
        # 还原形状
        return out.reshape(N, C, H, W)
    
    def backward(self, grad):
        # 接收输入形状
        N, C, H, W = self.input_shape
        # 展平后两个维度
        grad = grad.reshape(N, C, H*W)
        # 传入父类反向传播
        grad = super().backward(grad)
        # 还原形状
        return grad.reshape(N, C, H, W)

---

Dropout层

封装

class Dropout(Module):
    def __init__(self, p=0.5):
        """
        Args:
            p: 神经元被置零的概率
        """
        super().__init__()
        
        self.p = p
        self.mask = None
    
    def forward(self, x):
        # 评估模式不使用Dropout
        if not self.training or self.p == 0:
            return x
        
        # 生成掩码，保留概率为1 - p
        keep_prob = 1 - self.p
        self.mask = np.random.binomial(1, keep_prob, size=x.shape) / keep_prob
        
        return x * self.mask
    
    def backward(self, grad):
        # 评估模式不使用Dropout
        if not self.training or self.p == 0:
            return grad
        
        # 反向传播时，梯度通过相同的掩码
        return grad * self.mask
    
    def __call__(self, x):
        return self.forward(x)

    def __repr__(self):
        return self.__class__.__name__ + f"(p={self.p})"

测试

%matplotlib inline

# 数据点满足非线性关系
x = np.linspace(0, 1, 500).reshape(-1, 1)
y = 2 * x**3 + 0.2* np.random.randn(500).reshape(-1, 1)

plt.scatter(x, y)
plt.show()

​

​

# 定义模型和损失函数
model = Sequential(
    Linear(1, 30),
    Tanh(),
    Dropout(p=0.2),
    Linear(30, 15),
    Tanh(),
    Dropout(p=0.2),
    Linear(15, 1),
)
criterion = MSELoss()

optimizer = Adam(params=model.parameters(), lr=1e-2)

model.train()
# 训练流程
for epoch in range(1000):
    y_pred = model(x)
    loss, grad = criterion(y_pred, y)
    model.backward(grad)
    optimizer.step()
    optimizer.zero_grad()

    if(epoch % 200 == 0):
        print(loss)

0.05895352855605514
0.05955724161945543
0.05435588561688262
0.05203513368390939
0.052702349514423374

%matplotlib inline

model.eval()
# 检验拟合效果
x_plot = np.linspace(0, 1.2, 50).reshape(-1, 1)
plt.plot(x_plot, model(x_plot), c='r')
plt.scatter(x, y)
plt.show()

​

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