用数学方法解析复值神经网络的决策机制,提升可解释性与概率校准。
Newton-Puiseux Analysis for Interpretability and Calibration of Complex-Valued Neural Networks
- 基于牛顿-普瓦索展开构建局部多项式代理模型,捕捉不确定输入处的决策几何。
- 通过分支描述符(指数、重数、方向)定位引发类别翻转的敏感方向,实现精准校准。
- 无需修改网络结构,适用于任意复数逻辑输出的网络,适合医疗与无线信号场景。
复值神经网络(CVNN)在处理具有相位敏感性的信号(如心电图、雷达/声纳、无线I/Q流)方面表现优异,但其可解释性与概率校准仍不足。本文提出牛顿-普瓦索框架,通过在不确定输入附近拟合一个带尖点感知的小型多项式代理模型来分析已训练CVNN的局部决策几何,并利用牛顿-普瓦索展开对代理模型进行因式分解,获得解析的分支描述符(包括指数、重数和方向)。这些描述符提供相位对齐的引导方向,能诱发原始网络的类别翻转,并支持一种基于重数引导的温度调整以改进校准。我们阐明了代理模型有效的假设与诊断指标,揭示了由分段全纯激活函数(如modReLU)引起的潜在失效模式。该相位感知分析在两个真实案例研究中超越控制基准——即MIT-BIH心律失常(ECG)数据集与RadioML 2016.10a(无线调制)——相比未校准Softmax与标准后处理基线显著提升预期校准误差(Expected Calibration Error)。同时提供了置信区间、非参数检验,并量化了分支重数估计不准确带来的敏感性。该方法无需修改网络架构,适用于任何将复数逻辑转换为实数模的CVNN。
原文摘要 · Abstract (English)
Complex-valued neural networks (CVNNs) are particularly suitable for handling phase-sensitive signals, including electrocardiography (ECG), radar/sonar, and wireless in-phase/quadrature (I/Q) streams. Nevertheless, their \emph{interpretability} and \emph{probability calibration} remain insufficiently investigated. In this work, we present a Newton--Puiseux framework that examines the \emph{local decision geometry} of a trained CVNN by (i) fitting a small, kink-aware polynomial surrogate to the \emph{logit difference} in the vicinity of uncertain inputs, and (ii) factorizing this surrogate using Newton--Puiseux expansions to derive analytic branch descriptors, including exponents, multiplicities, and orientations. These descriptors provide phase-aligned directions that induce class flips in the original network and allow for a straightforward, \emph{multiplicity-guided} temperature adjustment for improved calibration. We outline assumptions and diagnostic measures under which the surrogate proves informative and characterize potential failure modes arising from piecewise-holomorphic activations (e.g., modReLU). Our phase-aware analysis identifies sensitive directions and enhances Expected Calibration Error in two case studies beyond a controlled $\C^2$ synthetic benchmark -- namely, the MIT--BIH arrhythmia (ECG) dataset and RadioML 2016.10a (wireless modulation) -- when compared to uncalibrated softmax and standard post-hoc baselines. We also present confidence intervals, non-parametric tests, and quantify sensitivity to inaccuracies in estimating branch multiplicity. Crucially, this method requires no modifications to the architecture and applies to any CVNN with complex logits transformed to real moduli.
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