Abstract
The theory of spectral approximants presents a precise geometric way of specifying approximants. The theory was initiated by Halmos [22] and later extended to the context of \(\mathcal{C}_{p}\) by Bouldin [11] and Bhatia [8]. More recently the related concept of numerical range approximant was introduced [25].
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Maher, P.J. (2017). Spectral, and Numerical Range, Approximants. In: Operator Approximant Problems Arising from Quantum Theory. Birkhäuser, Cham. https://doi.org/10.1007/978-3-319-61170-9_5
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DOI: https://doi.org/10.1007/978-3-319-61170-9_5
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