Signed Talaska formula for perfectly oriented networks on surfaces

From papers

Let N=(V,E)N=(V,E) be a perfectly oriented network embedded on a closed orientable surface with boundary. Let B(N,{xe}eE)B(N,\{x_e\}_{e\in E}) be its boundary measurement matrix, let II and JJ be boundary index sets with JKJ\subseteq K and I=J|I|=|J|, and let FI,J(N)\mathcal{F}_{I,J}(N) and C(N)\mathcal{C}(N) denote the corresponding families of flows and cycles. For a flow or cycle, write wt\operatorname{wt} for its weight.

Signed Talaska formula. There exists a map

σ:FI,J(N)C(N){±1}\sigma:\mathcal{F}_{I,J}(N)\cup\mathcal{C}(N)\longrightarrow\{\pm1\}

such that

ΔI,J(B(N,{xe}eE))=FFI,J(N)σ(F)wt(F)CC(N)σ(C)wt(C).\Delta_{I,J}\bigl(B(N,\{x_e\}_{e\in E})\bigr)=\frac{\sum_{\mathbf{F}\in\mathcal{F}_{I,J}(N)}\sigma(\mathbf{F})\operatorname{wt}(\mathbf{F})}{\sum_{\mathbf{C}\in\mathcal{C}(N)}\sigma(\mathbf{C})\operatorname{wt}(\mathbf{C})}.

This conjecture extends Talaska's subtraction-free formula from networks on a disk to perfectly oriented networks on arbitrary closed orientable surfaces with boundary, where signs are required to account for the topology.

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Sources & referencesView supporting material

Primary source

John Machacek, “Boundary Measurement Matrices for Directed Networks on Surfaces”, arXiv:1609.07525 (2017).

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