Borcea's normal-matrix invertibility conjecture
Let be a normal matrix, let be an orthonormal basis, and let denote the orthogonal projection onto . Write
for the corresponding compressions.
Borcea's normal-matrix invertibility conjecture. If every eigenvalue of every lies outside the unit disk and
for all , then 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.
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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