test: add convergence test for non-strctily-increasing squeeze morph

Author: ycexiao

src/diffpy/morph/morphs/morphsqueeze.py

@@ -100,9 +100,12 @@ def _set_squeeze_info(self, x, x_sorted):
                     "and stretch parameter for a1."
                 )
             else:
-                overlapping_regions = self.get_overlapping_regions(x)
-                self.squeeze_info["monotonic"] = False
-                self.squeeze_info["overlapping_regions"] = overlapping_regions
+                if list(x) != list(x_sorted[::-1]):
+                    overlapping_regions = self.get_overlapping_regions(x)
+                    self.squeeze_info["monotonic"] = False
+                    self.squeeze_info["overlapping_regions"] = (
+                        overlapping_regions
+                    )
 
     def _sort_squeeze(self, x, y):
         """Sort x,y according to the value of x."""

tests/test_morphsqueeze.py

@@ -173,10 +173,64 @@ def test_morphsqueeze_extrapolate(
         single_morph(parser, opts, pargs, stdout_flag=False)
 
 
+@pytest.mark.parametrize(
+    "squeeze_coeffs, x_morph",
+    [
+        ({"a0": 0.01, "a1": -0.99, "a2": 0.01}, np.linspace(-1, 1, 101)),
+    ],
+)
+def test_sort_squeeze(user_filesystem, squeeze_coeffs, x_morph):
+    x_target = x_morph
+    y_target = np.sin(x_target)
+    coeffs = [squeeze_coeffs[f"a{i}"] for i in range(len(squeeze_coeffs))]
+    squeeze_polynomial = Polynomial(coeffs)
+    x_squeezed = x_morph + squeeze_polynomial(x_morph)
+    # non-strictly-monotonic
+    assert not np.all(np.diff(np.sign(np.diff(x_squeezed))) == 0)
+    # outcome converges when --check-increase is not used
+    y_morph = np.sin(x_squeezed)
+    morph = MorphSqueeze()
+    morph.squeeze = squeeze_coeffs
+    with pytest.warns() as w:
+        moreph_results = morphpy.morph_arrays(
+            np.array([x_morph, y_morph]).T,
+            np.array([x_target, y_target]).T,
+            squeeze=[0.01, -0.99, 0.01],
+        )
+    assert w[0].category is UserWarning
+    actual_wmsg = " ".join([str(w[i].message) for i in range(len(w))])
+    expected_wmsg = (
+        "Warning: The squeeze morph has interpolated your morphed "
+        "function from a non-monotonically increasing grid. "
+    )
+    assert expected_wmsg in actual_wmsg
+    expected_coeffs = coeffs
+    actual_coeffs = [
+        moreph_results[0]["squeeze"][f"a{i}"]
+        for i in range(len(moreph_results[0]["squeeze"]))
+    ]
+    # program exits when --check-increase is used
+    assert np.allclose(actual_coeffs, expected_coeffs, rtol=1e-2)
+    with pytest.raises(SystemExit) as excinfo:
+        morphpy.morph_arrays(
+            np.array([x_morph, y_morph]).T,
+            np.array([x_target, y_target]).T,
+            squeeze=[0.01, -1, 0.01],
+            check_increase=True,
+        )
+    actual_emsg = str(excinfo.value)
+    expected_emsg = "2"
+    assert expected_emsg == actual_emsg
+
+
 @pytest.mark.parametrize(
     "squeeze_coeffs, x_morph",
     [
         ({"a0": -1, "a1": -1, "a2": 2}, np.linspace(-1, 1, 101)),
+        (
+            {"a0": -1, "a1": -1, "a2": 0, "a3": 0, "a4": 2},
+            np.linspace(-1, 1, 101),
+        ),
     ],
 )
 def test_sort_squeeze_bad(user_filesystem, squeeze_coeffs, x_morph):
@@ -267,7 +321,7 @@ def test_sort_squeeze_bad(user_filesystem, squeeze_coeffs, x_morph):
         # x[-1] > x[0], monotonically decreasing regions are overlapping
         ([0, 10, 7, 12], [[7, 10]]),
         # x[-1] < x[0], monotonically increasing regions are overlapping
-        ([0, 5, 2, 4, -10], [[0, 5], [2, 4]])
+        ([0, 5, 2, 4, -10], [[0, 5], [2, 4]]),
     ],
 )
 def test_get_overlapping_regions(turning_points, expected_overlapping_regions):