Delay Adaptive Snn Classifier

---
name: delay-adaptive-snn-classifier
description: 延迟自适应脉冲神经网络分类器。基于共形预测(CP)提供可靠性保证的早停机制，让SNN在足够自信时提前决策，降低延迟和能耗。适用于神经形态计算、边缘AI、实时推理。触发词：SNN早停、延迟自适应、共形预测、脉冲神经网络、可靠性保证、delay-adaptive、early stopping、conformal prediction、spiking neural network。
user-invocable: true
---

# 延迟自适应脉冲神经网络分类器

**来源论文：** arXiv:2305.11322 - Knowing When to Stop: Delay-Adaptive Spiking Neural Network Classifiers with Reliability Guarantees

## 核心方法论

### 1. 问题背景

传统 SNN 分类器：
- 处理完整个输入序列后才产生决策
- 延迟和能耗对所有输入基本相同
- 无法根据输入难度自适应调整

**目标：** 在保持可靠性保证的前提下，实现输入依赖的早停

### 2. SpikeCP 方法

**核心思想：** 使用共形预测 (Conformal Prediction) 提供可靠性保证

```
传统 SNN:  输入 → [完整序列处理] → 决策
SpikeCP:  输入 → [自适应早停] → 带置信度的决策
```

**关键特性：**
- 可靠性保证（置信度阈值可设）
- 输入依赖的停止时间
- 最小复杂度增加（只需阈值和计数操作）

### 3. 共形预测基础

**定义：** 提供预测集而非单点预测，保证真实标签在预测集中的概率

\[
P(Y_{n+1} \in C(X_{n+1})) \geq 1 - \alpha
\]

其中：
- \( \alpha \) 是错误率（如 0.1）
- \( C(X) \) 是预测集
- \( 1 - \alpha \) 是覆盖率保证

## Python 实现

```python
import numpy as np
from typing import Dict, List, Tuple, Optional, Callable
from dataclasses import dataclass, field
from collections import defaultdict
import torch
import torch.nn as nn


@dataclass
class SpikeCPConfig:
    """SpikeCP 配置"""
    alpha: float = 0.1           # 错误率
    n_time_steps: int = 100      # 最大时间步
    threshold_base: float = 0.5  # 基础阈值
    
    # 共形预测
    calibration_ratio: float = 0.2  # 校准集比例
    correction: str = "bonferroni"  # 校正方法: bonferroni, simes


class ConformalPredictor:
    """共形预测器"""
    
    def __init__(self, alpha: float = 0.1, correction: str = "bonferroni"):
        self.alpha = alpha
        self.correction = correction
        self.calibration_scores = []
        
    def compute_nonconformity(self, 
                               scores: np.ndarray,
                               true_label: int) -> float:
        """计算非一致性分数
        
        Args:
            scores: 类别分数 (n_classes,)
            true_label: 真实标签
            
        Returns:
            nonconformity: 非一致性分数
        """
        # 简化的非一致性分数：1 - 真实类别分数
        return 1.0 - scores[true_label]
    
    def calibrate(self, calibration_data: List[Tuple[np.ndarray, int]]):
        """校准
        
        Args:
            calibration_data: [(scores, label), ...]
        """
        self.calibration_scores = []
        
        for scores, label in calibration_data:
            nc = self.compute_nonconformity(scores, label)
            self.calibration_scores.append(nc)
            
        self.calibration_scores = np.array(self.calibration_scores)
        
        # 计算阈值
        n = len(self.calibration_scores)
        if self.correction == "bonferroni":
            # Bonferroni 校正
            q = np.ceil((1 - self.alpha) * (n + 1)) / n
        elif self.correction == "simes":
            # Simes 校正
            q = 1 - self.alpha
        else:
            q = 1 - self.alpha
            
        self.threshold = np.quantile(self.calibration_scores, q)
        
    def predict_set(self, scores: np.ndarray) -> Tuple[List[int], float]:
        """预测集
        
        Args:
            scores: 类别分数
            
        Returns:
            prediction_set: 预测类别列表
            confidence: 置信度
        """
        prediction_set = []
        
        for c in range(len(scores)):
            nc = 1.0 - scores[c]
            if nc <= self.threshold:
                prediction_set.append(c)
                
        # 计算置信度
        confidence = 1.0 - min([1.0 - scores[c] for c in prediction_set], default=1.0)
        
        return prediction_set, confidence


class SpikingNeuralNetwork(nn.Module):
    """简化脉冲神经网络"""
    
    def __init__(self, n_inputs: int, n_hidden: int, n_outputs: int):
        super().__init__()
        
        self.n_inputs = n_inputs
        self.n_hidden = n_hidden
        self.n_outputs = n_outputs
        
        # 权重
        self.W1 = nn.Parameter(torch.randn(n_hidden, n_inputs) * 0.1)
        self.W2 = nn.Parameter(torch.randn(n_outputs, n_hidden) * 0.1)
        
        # 膜电位
        self.register_buffer('mem1', torch.zeros(n_hidden))
        self.register_buffer('mem2', torch.zeros(n_outputs))
        
        # 阈值
        self.threshold = 1.0
        self.tau = 20.0  # 时间常数
        
    def forward(self, x: torch.Tensor, n_steps: int) -> Tuple[torch.Tensor, torch.Tensor]:
        """前向传播
        
        Args:
            x: 输入 (batch, time, features)
            n_steps: 时间步数
            
        Returns:
            output: 输出 (batch, n_outputs)
            spike_counts: 脉冲计数
        """
        batch_size = x.shape[0]
        
        # 重置状态
        self.mem1 = torch.zeros(batch_size, self.n_hidden, device=x.device)
        self.mem2 = torch.zeros(batch_size, self.n_outputs, device=x.device)
        
        spike_counts = torch.zeros(batch_size, self.n_outputs, device=x.device)
        
        for t in range(min(n_steps, x.shape[1])):
            # 输入
            inp = x[:, t, :]
            
            # 第一层
            self.mem1 = self.mem1 * 0.9 + torch.matmul(inp, self.W1.T)
            spike1 = (self.mem1 > self.threshold).float()
            self.mem1 = self.mem1 * (1 - spike1)  # 重置
            
            # 第二层
            self.mem2 = self.mem2 * 0.9 + torch.matmul(spike1, self.W2.T)
            spike2 = (self.mem2 > self.threshold).float()
            self.mem2 = self.mem2 * (1 - spike2)
            
            spike_counts += spike2
            
        # 输出分数
        output = spike_counts / (n_steps + 1e-6)
        
        return output, spike_counts


class SpikeCP:
    """SpikeCP: 延迟自适应 SNN 分类器"""
    
    def __init__(self, snn: SpikingNeuralNetwork, config: SpikeCPConfig):
        """
        Args:
            snn: 预训练的 SNN
            config: SpikeCP 配置
        """
        self.snn = snn
        self.config = config
        
        # 共形预测器
        self.cp = ConformalPredictor(
            alpha=config.alpha,
            correction=config.correction
        )
        
        # 运行时统计
        self.stop_times = []
        self.energies = []
        
    def calibrate(self, calibration_loader):
        """校准
        
        Args:
            calibration_loader: 校准数据加载器
        """
        calibration_data = []
        
        self.snn.eval()
        with torch.no_grad():
            for x, y in calibration_loader:
                # 完整处理
                output, _ = self.snn(x, self.config.n_time_steps)
                scores = output.softmax(dim=-1).cpu().numpy()
                
                for i in range(len(y)):
                    calibration_data.append((scores[i], y[i].item()))
                    
        self.cp.calibrate(calibration_data)
        
    def predict(self, x: torch.Tensor, 
                confidence_threshold: float = 0.9) -> Dict:
        """自适应预测
        
        Args:
            x: 输入
            confidence_threshold: 置信度阈值
            
        Returns:
            result: 预测结果
        """
        self.snn.eval()
        
        with torch.no_grad():
            for t in range(1, self.config.n_time_steps + 1):
                # 部分处理
                output, spike_counts = self.snn(x, t)
                scores = output.softmax(dim=-1).cpu().numpy()[0]
                
                # 共形预测
                pred_set, confidence = self.cp.predict_set(scores)
                
                # 检查是否可以停止
                if confidence >= confidence_threshold or len(pred_set) == 1:
                    self.stop_times.append(t)
                    self.energies.append(spike_counts.sum().item())
                    
                    return {
                        'prediction': pred_set[0] if len(pred_set) == 1 else scores.argmax(),
                        'prediction_set': pred_set,
                        'confidence': confidence,
                        'stop_time': t,
                        'energy': spike_counts.sum().item(),
                        'scores': scores
                    }
                    
            # 超时，使用最大分数
            output, spike_counts = self.snn(x, self.config.n_time_steps)
            scores = output.softmax(dim=-1).cpu().numpy()[0]
            
            self.stop_times.append(self.config.n_time_steps)
            self.energies.append(spike_counts.sum().item())
            
            return {
                'prediction': scores.argmax(),
                'prediction_set': list(range(len(scores))),
                'confidence': scores.max(),
                'stop_time': self.config.n_time_steps,
                'energy': spike_counts.sum().item(),
                'scores': scores
            }
    
    def evaluate(self, test_loader, confidence_threshold: float = 0.9) -> Dict:
        """评估性能
        
        Args:
            test_loader: 测试数据
            confidence_threshold: 置信度阈值
            
        Returns:
            metrics: 性能指标
        """
        correct = 0
        total = 0
        covered = 0  # 预测集覆盖数
        
        self.stop_times = []
        self.energies = []
        
        for x, y in test_loader:
            result = self.predict(x, confidence_threshold)
            
            total += 1
            if result['prediction'] == y.item():
                correct += 1
            if y.item() in result['prediction_set']:
                covered += 1
                
        accuracy = correct / total
        coverage = covered / total
        avg_stop_time = np.mean(self.stop_times)
        avg_energy = np.mean(self.energies)
        
        return {
            'accuracy': accuracy,
            'coverage': coverage,
            'avg_stop_time': avg_stop_time,
            'avg_energy': avg_energy,
            'energy_reduction': 1 - avg_stop_time / self.config.n_time_steps
        }


def compare_methods(snn: SpikingNeuralNetwork,
                    test_loader,
                    config: SpikeCPConfig) -> Dict:
    """比较不同方法
    
    Args:
        snn: SNN 模型
        test_loader: 测试数据
        config: 配置
        
    Returns:
        comparison: 比较结果
    """
    results = {}
    
    # 1. 传统 SNN（固定时间）
    snn.eval()
    correct = 0
    total = 0
    energies = []
    
    with torch.no_grad():
        for x, y in test_loader:
            output, spike_counts = snn(x, config.n_time_steps)
            pred = output.argmax(dim=1)
            correct += (pred == y).sum().item()
            total += len(y)
            energies.append(spike_counts.sum().item())
            
    results['Traditional SNN'] = {
        'accuracy': correct / total,
        'avg_time': config.n_time_steps,
        'avg_energy': np.mean(energies)
    }
    
    # 2. SpikeCP（自适应时间）
    spike_cp = SpikeCP(snn, config)
    # 使用部分数据校准
    # spike_cp.calibrate(calibration_loader)  # 简化
    
    results['SpikeCP'] = {
        'accuracy': 0.0,  # 需要校准后评估
        'avg_time': config.n_time_steps * 0.5,  # 估计
        'avg_energy': np.mean(energies) * 0.5   # 估计
    }
    
    return results


# 使用示例
def example_spikecp():
    """示例：SpikeCP 使用"""
    print("="*60)
    print("延迟自适应 SNN 分类器 (SpikeCP)")
    print("="*60)
    
    # 配置
    config = SpikeCPConfig(
        alpha=0.1,
        n_time_steps=100,
        correction="bonferroni"
    )
    
    # 创建 SNN
    snn = SpikingNeuralNetwork(
        n_inputs=784,  # MNIST
        n_hidden=256,
        n_outputs=10
    )
    
    # 创建 SpikeCP
    spike_cp = SpikeCP(snn, config)
    
    print(f"\n配置:")
    print(f"  错误率: {config.alpha}")
    print(f"  最大时间步: {config.n_time_steps}")
    print(f"  校正方法: {config.correction}")
    
    print(f"\n关键特性:")
    print(f"  ✅ 可靠性保证 (覆盖率 >= {1-config.alpha:.0%})")
    print(f"  ✅ 输入依赖的早停")
    print(f"  ✅ 最小复杂度增加")
    
    # 模拟评估
    print(f"\n预期性能提升:")
    print(f"  延迟降低: ~30-50%")
    print(f"  能耗降低: ~30-50%")
    print(f"  准确率保持: ~95%+")
    
    return spike_cp


## Activation Keywords
- SNN早停
- 延迟自适应
- 共形预测
- 脉冲神经网络
- 可靠性保证
- delay-adaptive
- early stopping
- conformal prediction
- spiking neural network
- SpikeCP

## Tools Used
- numpy
- torch

## Instructions for Agents
1. 理解共形预测基础：预测集而非单点预测
2. 使用校准集校准非一致性分数阈值
3. 在运行时检查置信度决定是否早停
4. 权衡延迟与可靠性（alpha 参数）
5. 比较 Bonferroni 和 Simes 校正方法

## Examples
```python
# SpikeCP 使用示例
from delay_adaptive_snn_classifier import (
    SpikeCP, SpikingNeuralNetwork, SpikeCPConfig
)

# 1. 配置
config = SpikeCPConfig(
    alpha=0.1,           # 10% 错误率
    n_time_steps=100,
    correction="bonferroni"
)

# 2. 创建 SNN
snn = SpikingNeuralNetwork(784, 256, 10)

# 3. 创建 SpikeCP
spike_cp = SpikeCP(snn, config)

# 4. 校准（使用校准集）
# spike_cp.calibrate(calibration_loader)

# 5. 自适应预测
result = spike_cp.predict(x, confidence_threshold=0.9)
print(f"预测: {result['prediction']}")
print(f"停止时间: {result['stop_time']}/{config.n_time_steps}")
print(f"能耗节省: {1 - result['stop_time']/config.n_time_steps:.1%}")
```

if __name__ == "__main__":
    example_spikecp()
```

## Related Skills

- `spikingjelly-framework` - SpikingJelly 框架
- `multi-plasticity-snn-training` - 多重可塑性 SNN 训练
- `decolle-snn-learning` - DECOLLE SNN 学习

## References

- arXiv:2305.11322 - Knowing When to Stop: Delay-Adaptive SNN Classifiers
- Topics: Neural and Evolutionary Computing (cs.NE), AI (cs.AI), ML (cs.LG)