Borcea's normal-matrix invertibility conjecture

From papers

Let AA be a normal matrix, let v(0),,v(n1)\mathbf v^{(0)},\dots,\mathbf v^{(n-1)} be an orthonormal basis, and let PP_\ell denote the orthogonal projection onto v()\mathbf v^{(\ell)}. Write

B=PAPB_\ell=P_\ell A P_\ell^*

for the corresponding compressions.

Borcea's normal-matrix invertibility conjecture. If every eigenvalue of every BB_\ell lies outside the unit disk and

(IP)AP1\|(I-P_\ell)AP_\ell\|\leq1

for all \ell, then AA is invertible.

The statement is identified as the matrix-theoretic reduction of Statement (i), and hence as equivalent to the 2-variance conjecture in the surrounding discussion. The source provides no proof or disproof.

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Sources & referencesView supporting material

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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