Line segments on the boundary of the numerical ranges of some tridiagonal matrices
Ilya M. Spitkovsky, Claire Thomas · Electronic Journal of Linear Algebra · 2015
Tridiagonal matrices are considered for which the main diagonal consists of zeroes, the sup-diagonal of all ones, and the entries on the sub-diagonal form a geometric progression. The criterion for the numerical range of such matrices to have line segments on its boundary is established, and the number and orientation of these segments is described.