Read one gas's fit where only its fit is needed

CHANGELOG.md

@@ -7,6 +7,12 @@ All notable changes are recorded here, in the style of
 
 ## Unreleased
 
+### Changed
+
+- `gas.ionisation.ionisation_parameters` and the compact models read their gas's own
+  fitted model, not all fifteen with their absorption terms (no value changed):
+  `ionisation_parameters("He")` takes half the time it did.
+
 ## 0.9.0 (2026-10-24)
 
 Models read only the data they need, so start-up is seconds to tens of seconds faster

src/optmat/gas/ionisation.py

@@ -328,9 +328,9 @@ def electronic_static_polarizability(gas: Gas | str) -> tuple[float, float, str]
         the model's name.
     """
     # Loaded here: the fitted models bring the whole dispersion chain.
-    from optmat.gas.models.fitted import FittedModel, fitted_models  # noqa: PLC0415
+    from optmat.gas.models.fitted import FittedModel, fitted_model  # noqa: PLC0415
 
-    model: FittedModel = fitted_models()[f"fit/{as_gas(gas).value}"]
+    model: FittedModel = fitted_model(f"fit/{as_gas(gas).value}")
     n_fitted = len(model.strengths) - model.n_fixed
     strengths = np.asarray(model.strengths[:n_fitted])
     energies = np.asarray(model.energies[:n_fitted])

src/optmat/gas/models/compact.py

@@ -51,7 +51,7 @@
 from optmat.gas.gases import Gas, as_gas
 from optmat.gas.infrared import gauss_rule
 from optmat.gas.models._defaults import defaults
-from optmat.gas.models.fitted import FittedModel, fitted_models
+from optmat.gas.models.fitted import FittedModel, fitted_model
 from optmat.identity import FrozenMapping
 
 __all__ = [
@@ -1179,7 +1179,7 @@ def _gap_note(self, wavelength: Float[np.ndarray, "*shape"]) -> str:
         """
         note = super()._gap_note(wavelength)
         values = np.ravel(np.asarray(wavelength, dtype=float))
-        parent = fitted_models()[self.parent]
+        parent = fitted_model(self.parent)
         theirs = ~_validity.outside(values, parent.intervals)
         if np.any(theirs & _validity.outside(values, self.intervals)):
             note += f"; {self.parent} is qualified there"
@@ -1193,7 +1193,7 @@ def _sources(self) -> tuple[str, ...]:
         tuple of str
             Sorted source ids.
         """
-        return fitted_models()[self.parent]._sources()
+        return fitted_model(self.parent)._sources()
 
 
 @functools.cache
@@ -1208,7 +1208,7 @@ def compact_models() -> dict[str, CompactModel]:
     models = {}
     for path in sorted(COMPACT_MODEL_DIRECTORY.glob("*.json")):
         record = json.loads(path.read_text(encoding="utf-8"))
-        parent = fitted_models()[record["parent"]]
+        parent = fitted_model(record["parent"])
         n_terms = len(parent.strengths) - parent.n_fixed + parent.n_rotational
         labels = [
             "compact (the parent's)" if kept else "compact" for kept in record["kept"]
@@ -1291,7 +1291,7 @@ def reproduction(model: CompactModel) -> dict[str, dict[str, float]]:
     # Imported here: the fitting code loads every dataset.
     from optmat.gas import fitting  # noqa: PLC0415
 
-    parent = fitted_models()[model.parent]
+    parent = fitted_model(model.parent)
     config = fitting.load_config(str(parent.record["name"]))
     start = len(model.strengths) - model.n_fixed + model.n_rotational
     compact = dataclasses.replace(
@@ -1569,7 +1569,7 @@ def _stated_error(
         largest difference in ``beta_2`` over the largest ``|beta_2|``, on the check
         grid over every interval.
     """
-    parent = fitted_models()[model.parent]
+    parent = fitted_model(model.parent)
 
     def sellmeier(x: Float[np.ndarray, " n"]) -> Float[np.ndarray, " n"]:
         """Return the Sellmeier form's ``n - 1``.
@@ -1696,7 +1696,7 @@ def coefficients(
         model=name,
         parent=model.parent,
         model_digest=model.identity.digest,
-        parent_digest=fitted_models()[model.parent].identity.digest,
+        parent_digest=fitted_model(model.parent).identity.digest,
         form=form,
         labels=tuple(model.labels[k] for k in order),
         kinds=tuple(str(x) for x in kinds),

tests/test_catalogue.py

@@ -108,12 +108,16 @@ def test_solprops_entry_points_never_load_the_catalogue():
 ionisation_parameters("Ar")
 raman_response("N2", 293.15)
 transport_model("Ar")
-print(optmat.datasets.sources.cache_info().currsize)
+from optmat.gas.molecular_ionisation_rates import molecular_rate_model
+molecular_rate_model("N2", 800e-9)
+from optmat.gas.models.fitted import fitted_models as fits
+print(optmat.datasets.sources.cache_info().currsize, fits.cache_info().currsize)
 """
     result = subprocess.run(
         [sys.executable, "-c", code], capture_output=True, text=True, check=True
     )
-    assert result.stdout.strip() == "0"
+    # Neither the catalogue nor every gas's fit (each with its absorption term).
+    assert result.stdout.split() == ["0", "0"]
 
 
 @pytest.mark.parametrize(