AI & ML
The reverse Ritz inclusion: computable bounds on the pseudospectra of an operator by those of a finite-rank compression
arXiv cs.NA0 views
arXiv:2610.30530v1 Announce Type: new Abstract: We consider a bounded operator on a separable complex Hilbert space, reached only through its action on vectors and that of its adjoint, and split it along a subspace of finite dimension into a compression, a far block acting on the complement, and the two couplings between them. Given upper bounds on the norms of the couplings and of the far block, we show that outside a disc a pseudospectrum of the operator lies in a pseudospectrum of the compression, with an explicit loss in the level; this reverses the classical inclusion of the Ritz values in a pseudospectrum of the operator. The same bounds, with the smallest singular value of the shifted compression, bound the resolvent of the operator, count its eigenvalues with algebraic multiplicity inside every contour outside the disc on which a computed inequality holds, and enclose its spectral projector; no normality, self-adjointness or positivity is used.
Source:https://arxiv.org/abs/2610.30530PreviousEntropy bounded compact stencil Runge-Kutta discontinuous Galerkin method for hyperbolic conservation lawsNextHigh-Order Fully Discrete Entropy-Stable DG Methods with Compact Explicit Single-Step Time Discretizations
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