Irreducibility of Full Multivariate Partial-Twuality Polynomials

Abstract

For each nonempty finite simple graph, we study five full multivariate partial-twuality polynomials defined using matrix ranks and coranks over $\mathbb{F}_2$. Over an arbitrary coefficient field $K$, we give a necessary and sufficient criterion for nontrivial factorization in the Laurent polynomial ring by additive separation of the exponent function across a nontrivial vertex partition. For $\bullet\in\{τ,δτ,τδ,δτδ\}$, the full multivariate partial-$\langle\bullet\rangle$ polynomial is irreducible in $K[z^{\pm1},\mathbf{u},\mathbf{v}]$ if and only if the graph is connected. For $δ$, we characterize the connected graphs whose polynomials are reducible by a condition on the parities of vertex degrees and of the numbers of common neighbors, and determine their irreducible factors. For each operation, the corresponding polynomial is irreducible in $K[z,\mathbf{u},\mathbf{v}]$ if and only if the graph is connected and at least one state has zero $z$-exponent. In particular, the full multivariate partial-$\langleδ\rangle$ polynomial is irreducible in $K[z,\mathbf{u},\mathbf{v}]$ if and only if the graph is connected and bipartite.