Adaptive grid on by default; finer auto cell size under it

ADAPTIVE_CELLS defaults to True (dialog checkbox stays; untick or
--no-adaptive for the uniform reference grid). With the adaptive grid
the auto cell sizer targets TARGET_CELLS_ADAPTIVE (8M fine cells,
~2x finer h) since unknowns no longer scale with the fine cell count -
memory of the masks/field arrays is the new bound.

The test suite pins ADAPTIVE_CELLS off via an autouse conftest fixture:
the exact-value tests define the uniform reference grid; adaptive tests
opt in per test.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -132,12 +132,14 @@ SWIG API. Requires KiCad **10.0.1+**.
   minimum-dissipation one, AC results are a rigorous **lower bound**.
   Rule of thumb for 70 µm foil: skin is negligible below ~300 kHz
   (δ = 173 µm at 142 kHz), ~+11 % at 1 MHz.
-- 5-point FDM per layer on an auto-sized shared grid (~2 M cells total
-  across layers by default). Direct sparse solve up to 500 k unknowns,
-  AMG-preconditioned CG (pyamg) above — Jacobi-CG if pyamg is missing.
-  Discretization error typically ≲ 2 % at defaults — halve the cell size
-  and compare to judge convergence.
-- **Adaptive cells** (dialog checkbox, off by default; `ADAPTIVE_CELLS`):
+- 5-point FDM per layer on an auto-sized shared grid (~2 M fine cells
+  with the uniform grid; ~8 M with the adaptive grid, whose unknown
+  count no longer scales with them). Direct sparse solve up to 500 k
+  unknowns, AMG-preconditioned CG (pyamg) above — Jacobi-CG if pyamg is
+  missing. Discretization error typically ≲ 2 % at defaults — halve the
+  cell size and compare to judge convergence.
+- **Adaptive cells** (dialog checkbox, **on by default**;
+  `ADAPTIVE_CELLS`):
   solves on a 2:1-balanced quadtree — fine cells at copper boundaries,
   electrodes, traces, via mouths and buildup, blocks up to
   `ADAPTIVE_MAX_CELL_UM` (2 mm) in plane interiors (`ADAPTIVE_GUARD`

conftest.py

@@ -1,4 +1,15 @@
 import os
 import sys
 
+import pytest
+
 sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
+
+
+@pytest.fixture(autouse=True)
+def _uniform_grid_default(monkeypatch):
+    """The exact-value test suite is the UNIFORM reference grid; the
+    adaptive default (config.ADAPTIVE_CELLS = True) is pinned off here.
+    Adaptive tests opt back in per test via monkeypatch."""
+    from fill_resistance import config
+    monkeypatch.setattr(config, "ADAPTIVE_CELLS", False)

fill_resistance/config.py

@@ -56,11 +56,16 @@ ELECTRODE_NEG_LAYER = "User.2"  # rectangles on this layer mark V- contact parts
 ALWAYS_REFILL = False           # refill zones even if KiCad says they are filled
 
 # --- Adaptive grid ---
-ADAPTIVE_CELLS = False          # solve on a 2:1-balanced quadtree: fine at
+ADAPTIVE_CELLS = True           # solve on a 2:1-balanced quadtree: fine at
                                 # copper boundaries/electrodes/features,
                                 # coarse plane interiors (dialog-toggleable).
-                                # Slight low bias (~0.5-1% on feature-dense
-                                # boards); large speed/memory wins on pours
+                                # With the deferred-correction pass the
+                                # deviation from the uniform grid is <0.03%
+                                # measured; untick for the reference grid
+TARGET_CELLS_ADAPTIVE = 8_000_000  # auto cell-size budget with the adaptive
+                                # grid: unknowns no longer scale with the
+                                # fine cell count, so the auto sizer picks
+                                # a ~2x finer h (memory-bound: masks/fields)
 ADAPTIVE_MAX_CELL_UM = 2000.0   # coarsest leaf edge length. The MINIMUM
                                 # element size is the grid cell size itself
                                 # (auto / dialog / CELL_UM_OVERRIDE). Rarely

fill_resistance/raster.py

@@ -97,7 +97,11 @@ def choose_cell_size(bbox_nm: tuple[int, int, int, int], nlayers: int) -> float:
             )
         h = config.CELL_UM_OVERRIDE * 1000.0
     else:
-        h = math.sqrt(w * ht * nlayers / config.TARGET_CELLS)
+        # the adaptive grid decouples unknowns from the fine cell count,
+        # so its auto sizing affords a larger fine-cell budget (finer h)
+        target = (config.TARGET_CELLS_ADAPTIVE if config.ADAPTIVE_CELLS
+                  else config.TARGET_CELLS)
+        h = math.sqrt(w * ht * nlayers / target)
         h = min(max(h, config.MIN_CELL_UM * 1000.0), config.MAX_CELL_UM * 1000.0)
 
     ncells = math.ceil(w / h) * math.ceil(ht / h) * nlayers

fill_resistance/standalone.py

@@ -47,9 +47,11 @@ def main(argv=None) -> int:
     ap.add_argument("--force-iterative", action="store_true",
                     help="use the iterative solver (AMG-CG, or Jacobi-CG "
                          "without pyamg) regardless of problem size")
-    ap.add_argument("--adaptive", action="store_true",
-                    help="solve on the adaptive quadtree grid (coarse "
-                         "plane interiors)")
+    ap.add_argument("--adaptive", action=argparse.BooleanOptionalAction,
+                    default=None,
+                    help="adaptive quadtree grid (coarse plane interiors); "
+                         "default: config (on). --no-adaptive forces the "
+                         "uniform reference grid")
     args = ap.parse_args(argv)
 
     if args.cell_um is not None:
@@ -58,8 +60,8 @@ def main(argv=None) -> int:
         config.INTERACTIVE = False
     if args.force_iterative:
         config.SPSOLVE_MAX_UNKNOWNS = 0
-    if args.adaptive:
-        config.ADAPTIVE_CELLS = True
+    if args.adaptive is not None:
+        config.ADAPTIVE_CELLS = args.adaptive
 
     problem = load_problem(args.dump)
     if args.strip_buildup:

metadata.json

@@ -2,7 +2,7 @@
     "$schema": "https://go.kicad.org/pcm/schemas/v2",
     "name": "Fill Resistance",
     "description": "DC/AC resistance of copper zone fills and traces between two contacts, single- or multi-layer with via coupling; current and power density maps.",
-    "description_full": "Computes the DC or AC resistance of copper zone fills and traces between two contacts (marker rectangles on User.1/User.2 and/or selected pads), single- or multi-layer: the chosen net's fills and tracks are solved as coupled finite-difference sheets linked by the net's via and through-hole-pad barrels; traces narrower than the grid become exact 1D resistor chains.\n\nShows per-layer rasterized maps, potential, current density and power density, reports per-via currents (via ampacity) and total dissipation at a selectable test current. At a user-set frequency the exact 1D foil/barrel skin-effect correction is applied (AC results are a rigorous lower bound). PNGs, a text summary and a re-solvable geometry dump are saved per run.\n\nNote: the first load builds the plugin's Python environment (numpy, scipy, pyamg, matplotlib, PySide6) and can take several minutes.",
+    "description_full": "Computes the DC or AC resistance of copper zone fills and traces between two contacts (marker rectangles on User.1/User.2 and/or selected pads), single- or multi-layer: the chosen net's fills and tracks are solved as coupled finite-difference sheets linked by the net's via and through-hole-pad barrels; traces narrower than the grid become exact 1D resistor chains, and an adaptive multi-resolution grid (fine at features, coarse plane interiors, deferred-corrected) keeps large boards fast.\n\nShows per-layer rasterized maps, potential, current density and power density, reports per-via currents (via ampacity) and total dissipation at a selectable test current. At a user-set frequency the exact 1D foil/barrel skin-effect correction is applied (AC results are a rigorous lower bound). PNGs, a text summary and a re-solvable geometry dump are saved per run.\n\nNote: the first load builds the plugin's Python environment (numpy, scipy, pyamg, matplotlib, PySide6) and can take several minutes.",
     "identifier": "th.co.b4l.fill-resistance",
     "type": "plugin",
     "author": {

tests/test_adaptive.py

@@ -165,6 +165,22 @@ def test_part_currents_and_ac(monkeypatch):
     assert ada.rs_ratios == ref.rs_ratios
 
 
+def test_auto_cell_size_finer_with_adaptive(monkeypatch):
+    """The auto sizer affords a larger fine-cell budget (finer h) when
+    the adaptive grid is on."""
+    from fill_resistance import raster
+    p = make_problem([([(0, 0), (300, 0), (300, 200), (0, 200)], [])],
+                     rect1_mm=(0, 90, 2, 110), rect2_mm=(298, 90, 300, 110))
+    monkeypatch.setattr(config, "ADAPTIVE_CELLS", False)
+    h_uniform = raster.choose_cell_size(p.copper_bbox(), 1)
+    monkeypatch.setattr(config, "ADAPTIVE_CELLS", True)
+    h_adaptive = raster.choose_cell_size(p.copper_bbox(), 1)
+    assert h_adaptive < h_uniform
+    assert h_adaptive == pytest.approx(
+        h_uniform / (config.TARGET_CELLS_ADAPTIVE
+                     / config.TARGET_CELLS) ** 0.5, rel=1e-9)
+
+
 def test_max_cell_size_respected(monkeypatch):
     from fill_resistance.adaptive import _max_block
     assert _max_block(100_000.0) == 16      # 2000 um / 100 um cells