Hermitian Lanczos method descriptor.

Usage

lanczos(
  max_subspace = NULL,
  max_restarts = NULL,
  block = 1L,
  check_stride = 0L,
  reorthogonalize = TRUE
)

max_subspace: Optional maximum active Krylov subspace size m. Must be at least k + 1. The native thick-restart path keeps the active basis bounded by this value across restart cycles.
max_restarts: Optional non-negative integer giving the maximum number of thick-restart cycles allowed before stopping with whatever has converged. Default 100L.
block: Native block size. 1L selects the scalar path; for a matrix-free operator this remains the reference Hermitian Lanczos boundary. Values greater than one select the native block Krylov path where supported, including real Hermitian matrix-free callbacks.
check_stride: Native block thick-restart mid-sweep convergence stride. 0L (default) evaluates convergence once per full sweep (legacy). A positive N evaluates convergence every N block iterations within a sweep, letting a warm start that converges after a few blocks stop early instead of paying a full cold-sized sweep. Mid-sweep checks never consume extra operator applications and never change results at check_stride = 0L. This control applies only to native block paths.
reorthogonalize: Whether to apply full reorthogonalization. The native path always reorthogonalizes (DGKS x2) and ignores this flag; it is preserved for the R reference solver's public API.

An eigencore_method descriptor selecting Lanczos iteration.