提出新几何框架,让无限维信息几何可计算且可解释。
An approach to Fisher-Rao metric for infinite dimensional non-parametric information geometry
- 用正交分解构造可观测协变量子空间的有限维信息矩阵。
- 证明了G-熵等于该矩阵迹,确立其为统计信息总量的几何不变量。
- 可用于评估高维数据内在维度与模型效率,适合可解释AI研究者。
非参数信息几何因无限维性长期面临不可计算的困境,源于费舍尔-罗信息度量现为泛函,难以定义其逆。本文提出新框架,通过切空间正交分解($T_fM = S \oplus S^{\perp}$),其中$S$表示可观测协变量子空间,导出可计算的协变量费舍尔信息矩阵(cFIM)${\bf G}_f$。通过证明迹定理:$H_G(f) = \text{Tr}({\bf G}_f)$,为此前提出的G-熵建立了严格基础,确认其为概率分布所捕获的总可解释统计信息的几何不变量。进一步揭示${\bf G}_f$与KL散度二阶导数(即曲率)的关联,引出协变量克拉默-罗下界(Covariate CRLB)。证明${\bf G}_f$等价于有效费舍尔信息矩阵,给出半参数估计器方差的理论极限。最后将该几何框架应用于流形假设,将其从启发式假设转化为可检验的cFIM秩亏条件;通过定义信息捕获比,提供高维数据内在维度的严格估计方法。本工作打通抽象信息几何与可解释人工智能需求之间的鸿沟,为非参数模型的统计覆盖与效率评估提供可计算路径。
原文摘要 · Abstract (English)
Being infinite dimensional, non-parametric information geometry has long faced an "intractability barrier" due to the fact that the Fisher-Rao metric is now a functional incurring difficulties in defining its inverse. This paper introduces a novel framework to resolve the intractability with an Orthogonal Decomposition of the Tangent Space ($T_fM = S \oplus S^{\perp}$), where $S$ represents an observable covariate subspace. Through the decomposition, we derive the Covariate Fisher Information Matrix (cFIM), denoted as ${\bf G}_f$, which is a finite-dimensional and computable representative of information extractable from the manifold's geometry. Significantly, by proving the Trace Theorem: $H_G(f) = \text{Tr}({\bf G}_f)$, we establish a rigorous foundation for the G-entropy previously introduced by us, thereby identifying it as a fundamental geometric invariant representing the total explainable statistical information captured by the probability distribution associated with a model. Furthermore, we establish a link between ${\bf G}_f$ and the second derivative (i.e. the curvature) of the KL-divergence, leading to the notion of Covariate Cramér-Rao Lower Bound(CRLB). We demonstrate that ${\bf G}_f$ is congruent to the Efficient Fisher Information Matrix, thereby providing fundamental limits of variance for semi-parametric estimators. Finally, we apply our geometric framework to the Manifold Hypothesis, lifting the latter from a heuristic assumption into a testable condition of rank-deficiency within the cFIM. By defining the Information Capture Ratio, we provide a rigorous method for estimating intrinsic dimensionality in high-dimensional data. In short, our work bridges the gap between abstract information geometry and the demand of explainable AI, by providing a tractable path for assessing the statistical coverage and the efficiency of non-parametric models.
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