Exclude only scipy 1.18.0, require pyccl>=3.3.5, fix the camb-backend C_ℓ at ℓ_min

cs_util/cosmo.py

@@ -716,8 +716,9 @@ def get_theo_c_ell(
             omch2_adj = camb_kwargs["omch2"] - pars.omeganu * (pars.H0 / 100) ** 2
             pars.set_cosmology(omch2=omch2_adj)
 
-        # Set up lensing source window
-        pars.min_l = ell.min()
+        # Set up lensing source window. CAMB's min_l is the scalar-C_ell floor
+        # (1 or 2 only), so leave it at its default; ell below ell.min() are
+        # computed and discarded by the interpolation.
         pars.set_for_lmax(ell.max())
 
         pars.SourceWindows = [

cs_util/tests/test_cosmology.py

@@ -387,6 +387,13 @@ def test_camb_backend_tomo(self, fast_ell_array, fast_two_bins_data):
         except ImportError:
             pytest.skip("CAMB not available")
 
+    def test_camb_backend_ell_range_independent(self, fast_redshift_data):
+        """CAMB C_ell at a given ell does not depend on the requested ell range."""
+        z, nz = fast_redshift_data
+        cl_wide = cosmology.get_theo_c_ell(np.array([10, 100, 1000]), z, nz, backend="camb")
+        cl_high = cosmology.get_theo_c_ell(np.array([100, 1000]), z, nz, backend="camb")
+        npt.assert_allclose(cl_high["W1xW1"], cl_wide["W1xW1"][1:], rtol=1e-6)
+
     def test_invalid_backend(self, fast_ell_array, fast_redshift_data):
         """Test error with invalid backend."""
         z, nz = fast_redshift_data

pyproject.toml

@@ -15,17 +15,15 @@ dependencies = [
 	"numpy>=1.26.4",
 	"matplotlib>=3.8.4",
 	"swig>=4.2.1",
-	# Cap scipy < 1.18: scipy 1.18 ported FITPACK from Fortran to C, changing
-	# RectBivariateSpline(scalar, scalar, grid=False) from a 0-d array to a
-	# shape-(1,) array. camb's BBN Y_He predictor then fails set_cosmology with
-	# "only 0-dimensional arrays can be converted to Python scalars", breaking
-	# every get_cosmo path (and pyccl's Boltzmann spline path likewise). camb
-	# 1.6.6 is unfixed; lift the cap when camb ships the scipy-1.18 fix. Mirrors
-	# the same cap in sp_validation.
-	"scipy>=1.13.0,<1.18",
+	# scipy 1.18.0 alone returns a shape-(1,) array from
+	# RectBivariateSpline(scalar, scalar, grid=False), which breaks the BBN Y_He
+	# predictor of camb < 2.0; scipy 1.18.1 restores the 0-d result.
+	"scipy>=1.13.0,!=1.18.0",
 	"vos>=3.6.1",
 	"keyring>=25.2.0",
-	"pyccl>=3.0.2",
+	# pyccl 3.3.5 is the first release whose boltzmann_camb path runs on camb 2
+	# (LSSTDESC/CCL#1303); pyccl declares no camb dependency, so the floor lives here.
+	"pyccl>=3.3.5",
 	"camb>=1.5.9",
 	"healpy>=1.16.0",
 	"healsparse>=1.8.0",