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Parcourir par sujet "Numerical range"

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    • Elliptical higher rank numerical range of some Toeplitz matrices 

      Adam M., Aretaki A., Spitkovsky I.M. (2018)
      The higher rank numerical range is described for a class of matrices which happen to be unitarily reducible to direct sums of (at most) 2-by-2 blocks. In particular, conditions are established under which tridiagonal ...

    • The generalized Levinger transformation 

      Adam, M.; Maroulas, J. (2010)
      In this paper, we present new results relating the numerical range of a matrix A with the generalized Levinger transformation L(A, alpha, beta) = alpha H(A) + beta S(A), where H(A) and S(A), are, respectively the Hermitian ...

    • On numerical ranges of the compressions of normal matrices 

      Adam, M. (2011)
      For an n x n normal matrix A, whose numerical range NR[A] is a k-polygon (k <= n), an n x (k - 1) isometry matrix P is constructed by a unit vector upsilon is an element of C(n), and NR[P*AP] is inscribed to NR[A]. In this ...

    • On the envelope of some classes of 3 by 3 matrices 

      Aretaki A., Chorianopoulos C. (2022)
      The envelope of a square complex matrix is a closed and bounded subset of the numerical range which contains the spectrum. We study the envelope of special classes of 3×3 matrices such as the nilpotent and the unitarily ...