Borcea's normal-matrix spectral-distance conjecture

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Let AA be an n×nn\times n normal matrix. Write W(A)W(A) for its numerical range, Σ(A)\Sigma(A) for its spectrum, and let AkA_k be the (n−1)×(n−1)(n-1)\times(n-1) matrix obtained by deleting the kkth row and column of AA. For compact sets, let HH denote the symmetrized Hausdorff distance.

Borcea's normal-matrix spectral-distance conjecture.

H(W(A),⋃k=1nΣ(Ak))≤min⁡c∈C∥A−cI∥.H\left(W(A),\bigcup_{k=1}^n\Sigma(A_k)\right)\leq\min_{c\in\mathbb C}\|A-cI\|.

This is presented as a matrix-theoretic generalization of Schmeisser's conjecture. The source provides no resolution.

References

Primary source

Dmitry Khavinson, Rajesh Pereira, Mihai Putinar, Edward B. Saff and Serguei Shimorin, “Borcea's variance conjectures on the critical points of polynomials”, arXiv:1010.5167 (2011).

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