Classify the extended Krylov variant used in ShaS13

Determine whether the extended Krylov basis-generation procedure used for constrained Sylvester equations in ShaS13 is a mixed-channel or split-channel approach.

Background

The paper classifies existing extended Krylov implementations according to whether applications of A and A^{-1} act on interleaved, mixed channels or on separate odd and even channels. This classification is important because the two approaches can exhibit different floating-point stability and loss-of-orthogonality behavior.

For ShaS13, the authors explain that a shifted inverse is needed because the original matrix is not invertible, but the source does not describe basis generation in sufficient detail to identify the channel structure. The classification therefore remains unresolved.