Hand each channel pair's factor-width-2 V to approx-chol 0.7

CHANGELOG.md

@@ -7,12 +7,14 @@ and this project follows [Semantic Versioning](https://semver.org/).
 
 ## [Unreleased]
 
-- Long weighted Gram diagonals and cross-table cells use compensated accumulation, avoiding roundoff-driven Laplacian validation failures and loss of signed cell contributions.
+- Long weighted Gram diagonals use compensated accumulation.
 
 ### Changed
 
 - **BREAKING:** `schwarz_precond::PartitionWeights::Uniform` is a unit variant; `PartitionWeights::len` and `is_empty` are removed. Uniform weights take their shape from `SubdomainCore::n_local`; only explicit weights carry a length. The serialized uniform variant no longer carries a count; the wire-format fixture moves v20 → v21; v20, v19 and v12 remain rejected-payload controls. The fixture number is not a runtime serialization envelope (#425).
-
+- Schwarz subdomains are factored by approx-chol 0.7 from each channel pair's factor-width-2 Gram factor `V`, one column per observation: sign folding, dominance scaling, floating detection and the Schur complement move into approx-chol, and each irreducible block is a subdomain (#481).
+- **BREAKING:** `ApproxSchurConfig::seed` (Python `seed=`) is removed; the Schur sampler draws from `ApproxCholConfig::seed`.
+- **BREAKING:** `ScalingConfig::tolerance` must lie in `[0, 1)`, else `BuildError::InvalidScalingTolerance`.
 - Levels with no cross-factor entries in a channel pair are batched into diagonal Schwarz subdomains per side instead of one subdomain each, cutting per-subdomain build and apply overhead without changing the preconditioner.
 - **BREAKING:** `ReductionStrategy` is removed: the `reduction` field of `PreconditionerConfig::Additive` and `::Adaptive`, Python's `reduction=` argument and `within.config.ReductionStrategy`, and the strategy argument of `SchwarzPreconditioner::new`/`with_n_dofs` with its `reduction_strategy()` getter. Overlapping subdomain outputs always sum in subdomain order (#472).
 - **BREAKING:** `schwarz_precond::LocalSolver::solve_local(x, workspace, allow_inner_parallelism)` solves in place, and the required `workspace_len()` replaces `scratch_size()`. `SubdomainEntry::{core, is_empty, scratch_size, apply_weighted_into_with_scratch, apply_weighted_into_atomic}`, `SubdomainCore::{restrict_weighted, prolongate_weighted_add, prolongate_weighted_add_atomic}`, `BuildError::ScratchSizeTooSmall` and `SolveError::Synchronization` are removed.

README.md

@@ -161,7 +161,7 @@ as `.build_duration_seconds`; both are preserved across pickling and reuse.
 | `LocalSolverConfig(approx_chol?, schur?, dense_threshold=24, scaling?)` | Schur reduction + approximate Cholesky. Omit `schur` for the library-default approximate variant; pass `schur=Schur.exact()` to request an exact Schur (slower, used for validation). |
 | `Schur.approximate(config?)` / `Schur.exact()` | Schur-reduction mode passed as `LocalSolverConfig(schur=...)`. |
 | `ApproxCholConfig(seed=0, split_merge=None)` | Approximate Cholesky parameters. |
-| `ApproxSchurConfig(seed=0, split=1)` | Approximate Schur complement sampling parameters. |
+| `ApproxSchurConfig(split=1)` | Approximate Schur complement sampling parameters; draws from `ApproxCholConfig.seed`. |
 
 ### Result types
 
@@ -284,7 +284,7 @@ across solves like any other.
 |---|---|---|
 | `within::config` | public | `LsmrOptions`, `PreconditionerConfig`, `LocalSolverConfig`, `SchurMode`, `ApproxCholConfig`, `ApproxSchurConfig`, `ScalingConfig` |
 | `within::error` | public | `WithinError`, `BuildError`, `SolveError` |
-| `block_elim` / `channel` / `csr_block` / `domain` / `linalg` / `operator` / `solver` | `pub(crate)` | implementation layers — public items are re-exported at the crate root |
+| `block_solver` / `channel` / `domain` / `linalg` / `operator` / `solver` | `pub(crate)` | implementation layers — public items are re-exported at the crate root |
 
 ## Project structure
 

benchmarks/_framework.py

@@ -207,13 +207,13 @@ def standard_solver_configs(
     """
     schur = LocalSolverConfig(
         approx_chol=ApproxCholConfig(seed=opts.seed),
-        schur=Schur.approximate(ApproxSchurConfig(seed=opts.seed)),
+        schur=Schur.approximate(ApproxSchurConfig()),
     )
     # "2-2": both densification knobs on — split_merge=2 (AC2 reduced-system
     # factorization) and split=2 (denser Schur clique-tree sampling).
     schur_2_2 = LocalSolverConfig(
         approx_chol=ApproxCholConfig(seed=opts.seed, split_merge=2),
-        schur=Schur.approximate(ApproxSchurConfig(seed=opts.seed, split=2)),
+        schur=Schur.approximate(ApproxSchurConfig(split=2)),
     )
     return [
         SolverConfig(

benchmarks/suites/ac_comparison.py

@@ -36,7 +36,7 @@
 def _schur(seed: int, split_merge: int | None) -> LocalSolverConfig:
     return LocalSolverConfig(
         approx_chol=ApproxCholConfig(seed=seed, split_merge=split_merge),
-        schur=Schur.approximate(ApproxSchurConfig(seed=seed)),
+        schur=Schur.approximate(ApproxSchurConfig()),
     )
 
 

benchmarks/suites/fixest_comparison.py

@@ -57,13 +57,13 @@ def run_fixest_comparison(opts: SuiteOptions) -> list[BenchmarkResult]:
     )
     approx_schur = LocalSolverConfig(
         approx_chol=ApproxCholConfig(seed=0, split_merge=8),
-        schur=Schur.approximate(ApproxSchurConfig(seed=0)),
+        schur=Schur.approximate(ApproxSchurConfig()),
     )
     # "2-2": both densification knobs on — split_merge=2 (AC2 factorization)
     # and split=2 (denser Schur clique-tree sampling).
     schur_2_2 = LocalSolverConfig(
         approx_chol=ApproxCholConfig(seed=0, split_merge=2),
-        schur=Schur.approximate(ApproxSchurConfig(seed=0, split=2)),
+        schur=Schur.approximate(ApproxSchurConfig(split=2)),
     )
 
     solver_configs = [

crates/within-py/src/config.rs

@@ -55,32 +55,27 @@ impl PyApproxCholConfig {
 #[pyclass(frozen, module = "within._within")]
 #[pyo3(name = "ApproxSchurConfig")]
 pub struct PyApproxSchurConfig {
-    #[pyo3(get)]
-    pub seed: u64,
     #[pyo3(get)]
     pub split: u32,
 }
 
 #[pymethods]
 impl PyApproxSchurConfig {
     #[new]
-    #[pyo3(signature = (seed=0, split=1))]
-    fn new(seed: u64, split: u32) -> PyResult<Self> {
+    #[pyo3(signature = (split=1))]
+    fn new(split: u32) -> PyResult<Self> {
         if split == 0 {
             return Err(pyo3::exceptions::PyValueError::new_err(
                 "split must be >= 1",
             ));
         }
-        Ok(Self { seed, split })
+        Ok(Self { split })
     }
 }
 
 impl PyApproxSchurConfig {
     pub(crate) fn to_native(&self) -> ApproxSchurConfig {
-        ApproxSchurConfig {
-            seed: self.seed,
-            split: self.split,
-        }
+        ApproxSchurConfig { split: self.split }
     }
 }
 
@@ -117,7 +112,7 @@ impl PySchur {
     fn __repr__(&self) -> String {
         match &self.inner {
             SchurMode::Approximate(cfg) => {
-                format!("Schur.approximate(seed={}, split={})", cfg.seed, cfg.split)
+                format!("Schur.approximate(split={})", cfg.split)
             }
             SchurMode::Exact => "Schur.exact()".to_string(),
         }

crates/within/Cargo.toml

@@ -12,7 +12,7 @@ categories.workspace = true
 
 [dependencies]
 schwarz-precond = { workspace = true, features = ["serde"] }
-approx-chol = { version = "0.6.0", features = ["serde"] }
+approx-chol = { version = "0.7.0", features = ["serde"] }
 serde = { workspace = true, features = ["rc"] }
 postcard.workspace = true
 ndarray = "0.17"