Ensure CoilCurvature and CoilTorsion are resolution independent

CHANGELOG.md

@@ -14,6 +14,7 @@ Performance Improvements
 Bug Fixes
 
 - Fixes bug in ``auglag`` optimizers which prevented them from accepting solver hyperparameters.
+- Adjusts the `quad_weights` of coil objectives of type `_broadcast_input = "node"` to ensure their outputs are roughly independent of grid resolution.
 - Fixes bug in modified Cholesky factorization used by the trust-region
   subproblems when the Gershgorin lower bound of the Hessian was exactly zero
   (e.g. a Hessian with an all-zero row), producing NaN steps in ``fmintr`` and

desc/objectives/_coils.py

@@ -220,9 +220,11 @@
         )
 
         _build_coilset_tree()
-        quad_weights = np.concatenate([g.spacing[:, 2] for g in grid])[
-            self._coilset_tree["objective_mask"]
-        ]
+        quad_weights = np.sqrt(
+            np.concatenate([g.spacing[:, 2] for g in grid])[
+                self._coilset_tree["objective_mask"]
+            ]
+        )
 
         if self._broadcast_input.lower() == "node":
             grid_nodes_unmasked = [

tests/test_objective_funs.py

@@ -3809,11 +3809,15 @@ def test_compute_scalar_resolution_coils(self, objective):
         f = np.zeros_like(self.res_array, dtype=float)
         for i, res in enumerate(self.res_array):
             obj = ObjectiveFunction(
-                objective(coilset, grid=LinearGrid(N=int(5 + 3 * res))),
+                objective(coilset, grid=LinearGrid(N=int(5 + 3 * res)), target=1),
                 use_jit=False,
             )
             obj.build(verbose=0)
             f[i] = obj.compute_scalar(obj.x())
+
+        # verify obj.compute_scalar is not zero, so the resolution test is meaningful
+        assert not np.isclose(f[-1], 0, atol=1e-8)
+
         np.testing.assert_allclose(f, f[-1], rtol=1e-2, atol=1e-12)
 
     @pytest.mark.unit