Defect Spaces and Gram Operators for Tensor-Valued Incidence Maps

Abstract

We study vector-valued incidence maps obtained from ordinary graph incidence maps by linear observation of the free vertex space. Let $\mathbb{F}$ be a field, $D = (X, E, s, t)$ a finite directed multigraph, $U$ an $\mathbb{F}$-vector space, and $ϕ: X \to U$ a vertex labeling with $\mathbb{F}$-linear extension $\hatϕ : \mathbb{F}^X \to U$. The vector-valued incidence map $\partial_ϕ: \mathbb{F}^E \to U$, $\partial_ϕ(\mathbf{1}_e) = ϕ(t(e)) - ϕ(s(e))$, factors as $\partial_ϕ= \hatϕ \circ B_D$, where $B_D$ is the classical incidence map of $D$. We prove the formula $\dim_{\mathbb{F}} \mathrm{Ker}(\partial_ϕ) = |E| - |X| + c(D) + δ_ϕ,$ where $c(D)$ is the number of weakly connected components of $D$ and $δ_ϕ:= \dim_{\mathbb{F}}(\mathrm{Im}(B_D) \cap \mathrm{Ker}(\hatϕ))$ is the defect invariant. We apply this framework to directed tensor-labeled hypergraphs $\mathcal{H} = (Q_0, Q_1, β)$, in which each hyperedge carries a pair of boundary tensors $(A_e, B_e)$ in the tensor algebra $T(\mathbb{F}^{Q_0})$, and prove that $δ(\mathcal{H}) = 0$ over any field for each of the six standard constructions, including symmetric encodings that degenerate in positive characteristic. Over $\mathbb{F} = \mathbb{R}$, the edge Gram operator $\mathcal{L} = \partial_β^* \partial_β$ has rank $|V_{\mathrm{macro}}| - c_{\mathrm{macro}} - δ(\mathcal{H})$, and its degree-truncated operators form a Loewner-monotone filtration whose rank increments equal the decrements of the defect filtration. We further realize the cycle space of every oriented hypergraph (in the sense of Reff--Rusnak) as $\mathrm{Ker}(\partial_β)$ within this framework, and exhibit a four-edge inclusion--exclusion example with $δ(\mathcal{H}) = 1$.