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>

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: