Fix is_supercell for left-handed input cells

seekpath/getpaths.py

@@ -166,9 +166,10 @@ def get_path(
           (the determinant is integer and gives the ratio in volume between
           the conventional and primitive cells)
         - ``volume_original_wrt_conv``: volume ratio of the user-provided cell
-          with respect to the the crystallographic conventional cell
+          with respect to the crystallographic conventional cell
         - ``volume_original_wrt_prim``: volume ratio of the user-provided cell
-          with respect to the the crystalloraphic primitive cell
+          with respect to the crystallographic primitive cell (both volume
+          ratios are negative if the user-provided cell is left-handed)
 
     :note: An :py:exc:`~seekpath.hpkot.EdgeCaseWarning` is issued for
         edge cases (e.g. if ``a==b==c`` for
@@ -421,7 +422,9 @@ def get_path_orig_cell(
         recipe=recipe,
     )
 
-    is_supercell = abs(res['volume_original_wrt_prim'] - 1) > 0.1
+    # The volume ratio is negative for a left-handed input cell, so only its
+    # magnitude says whether the cell is a supercell
+    is_supercell = abs(abs(res['volume_original_wrt_prim']) - 1) > 0.1
 
     if is_supercell:
         warnings.warn(

seekpath/hpkot/__init__.py

@@ -119,9 +119,10 @@ def get_path(
         - ``rotation_matrix``: rotation matrix in Cartesian space from the input
           cell to the standardized cell
         - ``volume_original_wrt_conv``: volume ratio of the user-provided cell
-          with respect to the the crystallographic conventional cell
+          with respect to the crystallographic conventional cell
         - ``volume_original_wrt_prim``: volume ratio of the user-provided cell
-          with respect to the the crystallographic primitive cell
+          with respect to the crystallographic primitive cell (both volume
+          ratios are negative if the user-provided cell is left-handed)
 
     :note: An :py:exc:`~seekpath.hpkot.EdgeCaseWarning` is issued for
         edge cases (e.g. if ``a==b==c`` for

tests/test_brillouinzone.py

@@ -24,7 +24,7 @@ def is_same_face(f1, f2):
 
     f1 and f2 should be a list of 3d points (i.e., a list of lists).
 
-    It also checks if the the coordinates are shifted (i.e. the first one is
+    It also checks if the coordinates are shifted (i.e. the first one is
         now the second, the second the third etc.). Tries also points in
         reversed order.
     """

tests/test_paths_hpkot.py

@@ -1002,6 +1002,38 @@ def test_nonstandard_cubic_supercell(self):
 
         self.assertEqual(res['spacegroup_international'], 'Pm-3m')
 
+    def test_left_handed_fcc(self):
+        """
+        Obtain the k-path for a left-handed primitive fcc cell, which is not
+        a supercell even though its volume ratio to the primitive cell is -1.
+        """
+        import warnings
+
+        from seekpath import SupercellWarning
+
+        cell = [[-3.0, 0.0, 3.0], [0.0, 3.0, 3.0], [-3.0, 3.0, 0.0]]
+        positions = [[0.0, 0.0, 0.0], [0.25, 0.25, 0.25]]
+        atomic_numbers = [1, 1]
+
+        # An improper rotation makes the cell left-handed
+        s = np.sin(0.3)
+        c = np.cos(0.3)
+        R = np.array([[-1.0, 0.0, 0.0], [0.0, c, s], [0.0, -s, c]])
+
+        cell = cell @ R
+        system = (cell, positions, atomic_numbers)
+        self.assertLess(np.linalg.det(cell), 0)
+
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter('always')
+            res = self.base_test(system)
+            self.assertEqual(res['is_supercell'], False)
+
+            relevant_w = [_ for _ in w if issubclass(_.category, SupercellWarning)]
+            self.assertEqual(relevant_w, [])
+
+        self.assertEqual(res['spacegroup_international'], 'Fd-3m')
+
     def test_no_symmetrization(self):
         """
         Test that symmetrization is not performed so that the k path is on
@@ -1089,22 +1121,16 @@ def test_path(self):  # pylint: disable=no-self-use
         res_standard = seekpath.get_explicit_k_path(system, recipe='hpkot')
 
         with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter('always')
             res_original = seekpath.get_explicit_k_path_orig_cell(
                 system, recipe='hpkot'
             )
-            self.assertEqual(res_original['is_supercell'], True)
+            # The cell is left-handed (because of the improper rotation R), but
+            # it is a primitive cell, not a supercell
+            self.assertEqual(res_original['is_supercell'], False)
 
-            # Checks on issued warnings
             relevant_w = [_ for _ in w if issubclass(_.category, SupercellWarning)]
-            self.assertEqual(
-                len(relevant_w),
-                1,
-                f'Wrong number of warnings issued! ({len(relevant_w)} instead of 1)',
-            )
-
-            check_string = 'The provided cell is a supercell: the returned'
-            if check_string is not None:
-                self.assertIn(check_string, str(relevant_w[0].message))
+            self.assertEqual(relevant_w, [])
 
         self.assertEqual(res_original['path'], res_standard['path'])
         self.assertEqual(res_original['augmented_path'], res_standard['augmented_path'])