Give useful error message when trying to pass decreasing a array to C…

…alculatorCosmology (#864)

* Give useful error message when trying to pass decreasing a array.

* Check Pk2D too.

pyccl/core.py

@@ -1276,6 +1276,11 @@ def _init_pklin(self, pk_linear):
                              "and 'delta_matter:delta_matter' "
                              "(at least)")
 
+        # Check that `a` is a monotonically increasing array.
+        if not np.array_equal(pk_linear['a'], np.sort(pk_linear['a'])):
+            raise ValueError("Input scale factor array in `pk_linear` is not "
+                             "monotonically increasing.")
+
         # needed for high-z extrapolation
         self.compute_growth()
 
@@ -1314,6 +1319,11 @@ def _init_pknl(self, pk_nonlin, has_nonlin_model):
         if (('a' not in pk_nonlin) or ('k' not in pk_nonlin)):
             raise ValueError("`pk_nonlin` must contain keys "
                              "'a' and 'k' (at least)")
+        # Check that `a` is a monotonically increasing array.
+        if not np.array_equal(pk_nonlin['a'], np.sort(pk_nonlin['a'])):
+            raise ValueError("Input scale factor array in `pk_nonlin` is not "
+                             "monotonically increasing.")
+
         if ((not has_nonlin_model) and
                 ('delta_matter:delta_matter' not in pk_nonlin)):
             raise ValueError("`pk_nonlin` must contain key "

pyccl/pk2d.py

@@ -72,6 +72,11 @@ def __init__(self, pkfunc=None, a_arr=None, lk_arr=None, pk_arr=None,
                 raise ValueError("If you do not provide a function, "
                                  "you must provide arrays")
 
+            # Check that `a` is a monotonically increasing array.
+            if not np.array_equal(a_arr, np.sort(a_arr)):
+                raise ValueError("Input scale factor array in `a_arr` is not "
+                                 "monotonically increasing.")
+
             pkflat = pk_arr.flatten()
             # Check dimensions make sense
             if (len(a_arr)*len(lk_arr) != len(pkflat)):

pyccl/tests/test_pk2d.py

@@ -54,6 +54,10 @@ def test_pk2d_init():
     assert_raises(
         ValueError, ccl.Pk2D, a_arr=aarr, lk_arr=lkarr, pk_arr=pkarr[1:])
 
+    # Scale factor is not monotonically increasing
+    assert_raises(
+        ValueError, ccl.Pk2D, a_arr=aarr[::-1], lk_arr=lkarr, pk_arr=pkarr)
+
 
 def test_pk2d_smoke():
     """Make sure it works once."""

pyccl/tests/test_power.py

@@ -292,6 +292,14 @@ def test_input_linpower_raises():
             n_s=0.965, sigma8=0.8,
             pk_linear=np.pi)
 
+    # a not increasing
+    with pytest.raises(ValueError):
+        ccl.CosmologyCalculator(
+            Omega_c=0.27, Omega_b=0.05, h=0.7,
+            n_s=0.965, sigma8=0.8,
+            pk_linear={'a': a_arr[::-1], 'k': k_arr,
+                       'delta_matter:delta_matter': pk_arr})
+
     # Dm x Dm not present
     with pytest.raises(ValueError):
         ccl.CosmologyCalculator(
@@ -527,6 +535,14 @@ def test_input_nonlin_raises():
             pk_nonlin={'a': a_arr, 'kk': k_arr,
                        'delta_matter;delta_matter': pk_arr})
 
+    # a not increasing
+    with pytest.raises(ValueError):
+        ccl.CosmologyCalculator(
+            Omega_c=0.27, Omega_b=0.05, h=0.7,
+            n_s=0.965, sigma8=0.8,
+            pk_nonlin={'a': a_arr[::-1], 'k': k_arr,
+                       'delta_matter:delta_matter': pk_arr})
+
     # delta_matter:delta_matter not present
     with pytest.raises(ValueError):
         ccl.CosmologyCalculator(