Fix failing axis limit test

desc/compute/_basis_vectors.py

@@ -3262,7 +3262,7 @@ def _periodic_grad_alpha(params, transforms, profiles, data, **kwargs):
     units_long="Inverse meters",
     description=(
         "Gradient of field line label, which is perpendicular to the field line, "
-        "periodic component"
+        "secular component"
     ),
     dim=3,
     params=[],

desc/integrals/basis.py

@@ -137,10 +137,15 @@ class FourierChebyshevSeries(IOAble):
 
     Examples
     --------
-    Let the magnetic field be B = ∇ρ × ∇α, x = α, and y = ζ. This basis can
-    will then parameterize maps in Clebsch coordinates. Passing in a sequence
-    of α values tracking the field line (see ``get_alpha``) to the
-    ``compute_cheb`` method will generate f along field lines.
+    Let the magnetic field be B = ∇ρ × ∇x. This basis will then parameterize
+    maps in Clebsch coordinates. Passing in a sequence of x values tracking
+    the field line (see ``get_alpha``) to the ``compute_cheb`` method will
+    generate a 1D parameterization of f along the field line.
+
+    This is useful to interpolate f ≝ θ and use the map x, ζ ↦ θ(x, ζ) to
+    compute quantities along field lines via evaluating Fourier series
+    parameterized in DESC computational coordinates θ, ζ, where the Fourier
+    transform is more condensed when NFP > 1.
 
     Notes
     -----

tests/test_axis_limits.py

@@ -18,7 +18,7 @@
 from desc.grid import LinearGrid
 from desc.integrals import surface_integrals_map
 from desc.objectives import GenericObjective, ObjectiveFunction
-from desc.utils import dot
+from desc.utils import dot, errorif
 
 # Unless mentioned in the source code of the compute function, the assumptions
 # made to compute the magnetic axis limit can be reduced to assuming that these
@@ -44,6 +44,7 @@
     "curvature_k1_zeta",
     "curvature_k2_rho",
     "curvature_k2_zeta",
+    "cvdrift",
     "e^helical",
     "e^theta",
     "e^theta_r",
@@ -63,10 +64,11 @@
     "g^tz_z",
     "g^aa",
     "g^ra",
+    "gbdrift",
     "grad(alpha)",
     "periodic(grad(alpha))",
-    "gbdrift",
-    "cvdrift",
+    "periodic(gbdrift)",
+    "periodic(cvdrift)",
     "|e^helical|",
     "|grad(theta)|",
     "<J*B> Redl",  # may not exist for all configurations
@@ -216,10 +218,10 @@ def assert_is_continuous(
         if name in not_continuous_limits:
             continue
         elif name in not_finite_limits:
-            assert (np.isfinite(data[name]).T != axis).all(), name
+            errorif(np.any(np.isfinite(data[name]).T == axis), AssertionError, msg=name)
             continue
         else:
-            assert np.isfinite(data[name]).all(), name
+            errorif(not np.isfinite(data[name]).all(), AssertionError, msg=name)
 
         if (
             data_index[p][name]["coordinates"] == ""
@@ -289,6 +291,9 @@ def test_limit_continuity(self):
             "iota_r": {"atol": 1e-6},
             "iota_num_rr": {"atol": 5e-5},
             "grad(B)": {"rtol": 1e-4},
+            "secular(alpha_r)": {"atol": 1e-4},
+            "secular(grad(alpha))": {"atol": 1e-4},
+            "secular(gbdrift)": {"atol": 1e-4},
         }
         zero_map = dict.fromkeys(zero_limits, {"desired_at_axis": 0})
         kwargs = weaker_tolerance | zero_map