Changes in version 0.1.0.9000                      

Performance fixes

  - The sparse commute solver now uses eigencore (>= 1.0.3) from CRAN as
    a required import, replacing optional RSpectra. Large masks no
    longer need a separate solver installation. Sparse solves use a
    fixed local RNG seed, check original-Laplacian residuals and
    orthogonality, and disable implicit dense fallback. The minimum R
    version is now 4.1, as required by eigencore.
  - rena_plus() (cluster4d(method = "rena_plus")) is no longer quadratic
    in the number of voxels. The ReNA coarsening walked each row of the
    column-compressed adjacency matrix with Armadillo's row iterator,
    which costs O(N) per row; it now walks the columns of the transpose,
    which visits the same neighbours in the same order. Labels are
    bit-identical to the previous implementation. On the 29,532-voxel
    neuroim2 mask (20 timepoints, n_clusters = 200) run time drops
    from 118 s to 0.5 s (#3).
  - commute_cluster() (cluster4d(method = "commute")) gains eigen_solver
    = c("auto", "dense", "sparse"). The dense path formed an N-by-N
    Laplacian and a full eigen() (O(N^2) memory, O(N^3) time; about 7 GB
    per dense copy on a 30,000-voxel mask) although only the ncomp
    smallest eigenpairs are used. Above 3,000 voxels "auto" now computes
    only those eigenpairs with shift-invert Lanczos; at or below 3,000
    voxels results are unchanged. The initial RSpectra implementation
    finished the 29,532-voxel mask in about 5 s (#3); that timing does
    not characterize the replacement eigencore backend. Dense and sparse
    solvers are compared against numerical oracles in the tests.

Continuous integration

  - The Native sanitizers workflow's asan job had failed since
    August 2026 without compiling the package:
    tools/run-native-sanitizers.sh preloaded the ASan runtime into GNU
    make, whose own strndup() calls ASan reported as
    heap-buffer-overflows under strict_string_checks=1. The runtime is
    now preloaded only into the R process that runs the smoke cases, and
    the script fails if ASan is not active there. No overflow was found
    in package code (#2).

Documentation and interface fixes

  - ?cluster4d now lists all 13 method values (adding corr_slic,
    rena_plus and commute) and no longer labels g3s as "recommended";
    method order is stated not to be a ranking. The "Algorithm
    Comparison" table now covers every method, reports measured speed
    tiers (SNIC is listed as slow on whole-brain masks because its k-NN
    gradient seeding dominates run time), and states which common
    arguments each method uses. The quick cluster4d() example now runs
    during checks (#1).
  - cluster4d_rena() and cluster4d_rena_plus() no longer show an
    inactive spatial_weight = 0.5 default in their usage. spatial_weight
    is no longer a formal argument; supplying it (now through ...) is
    still an error. Code that passed a fourth positional argument
    intending spatial_weight now binds it to max_iterations
    (cluster4d_rena()) or r (cluster4d_rena_plus()) (#1).