The polynomial inverse-factorization alternative for invertible noncommutative polynomial matrices

Let Kx\mathbb K\langle\underline{x}\rangle denote the free noncommutative polynomial algebra, let r=(pij)KxL×L\mathfrak r=(p_{ij})\in\mathbb K\langle\underline{x}\rangle^{L\times L} have noncommutative polynomial entries, and let a=(a1,,ad)Ad\underline{\mathfrak a}=(\mathfrak a_1,\ldots,\mathfrak a_d)\in\mathcal A^d. Assume that

r(a)=(pij(a))i,jAL×L\mathfrak r(\underline{\mathfrak a})=(p_{ij}(\underline{\mathfrak a}))_{i,j}\in\mathcal A^{L\times L}

is invertible. Polynomial inverse-factorization conjecture. There exist either noncommutative rational expressions S11,,SLLS_{11},\ldots,S_{LL} satisfying

ai,jdomA(Sij),\underline{\mathfrak a}\in\bigcap_{i,j}\operatorname{dom}_{\mathcal A}(S_{ij}),

or noncommutative polynomials S11,,SLLS_{11},\ldots,S_{LL}, such that (Sij(a))i,j(S_{ij}(\underline{\mathfrak a}))_{i,j} is invertible and there exist 1i,jL1\leq i,j\leq L for which

k=1Lpik(a)Skj(a)\sum_{k=1}^L p_{ik}(\underline{\mathfrak a})S_{kj}(\underline{\mathfrak a})

is invertible in A\mathcal A. The assertion is presented as an alternative formulation needed to prove the preceding matrix-inverse conjecture.

Sources & referencesView supporting material

Primary source

Motke Porat and Victor Vinnikov, “Realizations of non-commutative rational functions around a matrix centre, II: The lost-abbey conditions”, arXiv:2009.08527 (2022).

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