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| Format: | Preprint |
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2026
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| Online Access: | https://arxiv.org/abs/2604.17775 |
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| _version_ | 1866911606047244288 |
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| author | Pardo-Guerra, Sebastian Thapa, Anil Washburn, Jonathan |
| author_facet | Pardo-Guerra, Sebastian Thapa, Anil Washburn, Jonathan |
| contents | Let $G$ be a finite connected simple graph with a chosen orientation of its edges. For the edge potential $ψ(t)=\cosh t-1,$ we minimize $\sum_{e\in E^\to}ψ(z_e)$ over each affine class $ω+dC^0(G)\subset C^1(G)$. The minimizer is the unique representative satisfying the nonlinear coclosed equation $δ\sinh z=0,$ and hence defines a nonlinear selector $\Picc:C^1(G)\to C^1(G).$ We show that $\Picc$ is real analytic, identify its image as $\imop \Picc=\Mcc=\operatorname{arsinh}(\kerδ),$ and compute its differential as a weighted Hodge projector. In particular, $\Picc$ agrees with the ordinary Hodge projector $\PiH$ to first order at the origin, and the first nonlinear correction is cubic. Our main global theorem is a graph-theoretic criterion: for every admissible edge potential -- even, $C^2$, strictly convex, and non-quadratic -- the associated nonlinear selector coincides with $\PiH$ on all of $C^1(G)$ if and only if $G$ is a cactus graph. Finally, we work out the two-triangle graph, the smallest connected simple obstruction, and record a self-concordant Newton method for computing $\Picc$. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2604_17775 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | The Cactus Criterion: When Nonlinear Hodge Theory Reduces to Linear on Graphs Pardo-Guerra, Sebastian Thapa, Anil Washburn, Jonathan Combinatorics Geometric Topology 05C50, 05C75, 05E45 Let $G$ be a finite connected simple graph with a chosen orientation of its edges. For the edge potential $ψ(t)=\cosh t-1,$ we minimize $\sum_{e\in E^\to}ψ(z_e)$ over each affine class $ω+dC^0(G)\subset C^1(G)$. The minimizer is the unique representative satisfying the nonlinear coclosed equation $δ\sinh z=0,$ and hence defines a nonlinear selector $\Picc:C^1(G)\to C^1(G).$ We show that $\Picc$ is real analytic, identify its image as $\imop \Picc=\Mcc=\operatorname{arsinh}(\kerδ),$ and compute its differential as a weighted Hodge projector. In particular, $\Picc$ agrees with the ordinary Hodge projector $\PiH$ to first order at the origin, and the first nonlinear correction is cubic. Our main global theorem is a graph-theoretic criterion: for every admissible edge potential -- even, $C^2$, strictly convex, and non-quadratic -- the associated nonlinear selector coincides with $\PiH$ on all of $C^1(G)$ if and only if $G$ is a cactus graph. Finally, we work out the two-triangle graph, the smallest connected simple obstruction, and record a self-concordant Newton method for computing $\Picc$. |
| title | The Cactus Criterion: When Nonlinear Hodge Theory Reduces to Linear on Graphs |
| topic | Combinatorics Geometric Topology 05C50, 05C75, 05E45 |
| url | https://arxiv.org/abs/2604.17775 |