Eigenvalue realization conjecture for locally singular matrices in Sn,k\mathcal{S}^{n,k}

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Let H(ekn)H(e^n_k) denote the hyperbolicity cone of the elementary symmetric polynomial ekne^n_k, and let DG(n,k)DDG(n,k)D be a diagonal congruence of the matrix G(n,k)G(n,k) by a diagonal matrix DD. A vector λ\lambda has at most one negative entry if at most one of its coordinates is negative. Eigenvalue realization conjecture. If λ∈H(ekn)\lambda\in H(e^n_k), ekn(λ)=0e^n_k(\lambda)=0, and λ\lambda has at most one negative entry, then λ\lambda is a vector of eigenvalues for DG(n,k)DDG(n,k)D for some diagonal matrix DD. The conjecture asks whether these necessary spectral conditions are also sufficient for realizing the eigenvalue vector of a nonsingular locally singular matrix in Sn,k\mathcal{S}^{n,k}; the supplied text does not indicate that it has been resolved.

References

Primary source

Grigoriy Blekherman, Santanu S. Dey, Kevin Shu and Shengding Sun, “Hyperbolic Relaxation of k-Locally Positive Semidefinite Matrices”, arXiv:2012.04031 (2021).

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