From c84336878bdfb38c261094205ab5360949d6743d Mon Sep 17 00:00:00 2001
From: RemDelaporteMathurin <rdelaportemathurin@gmail.com>
Date: Fri, 27 Jan 2023 08:58:10 -0500
Subject: [PATCH] replace is_flat by a one-line check

---
 openmc/mesh.py                | 18 ++++--------------
 tests/unit_tests/test_mesh.py | 22 ----------------------
 2 files changed, 4 insertions(+), 36 deletions(-)

diff --git a/openmc/mesh.py b/openmc/mesh.py
index 3cdfc87f3b..60c5ade40d 100644
--- a/openmc/mesh.py
+++ b/openmc/mesh.py
@@ -433,8 +433,8 @@ class RegularMesh(StructuredMesh):
         cv.check_length('mesh lower_left', lower_left, 1, 3)
         self._lower_left = lower_left
 
-        if self.is_flat():
-            raise ValueError("mesh cannot be flat")
+        if self.upper_right is not None and any(np.isclose(self.upper_right, lower_left)):
+            raise ValueError("mesh cannot have zero thickness is any dimension")
 
     @upper_right.setter
     def upper_right(self, upper_right):
@@ -446,8 +446,8 @@ class RegularMesh(StructuredMesh):
             self._width = None
             warnings.warn("Unsetting width attribute.")
         
-        if self.is_flat():
-            raise ValueError("mesh cannot be flat")
+        if self.lower_left is not None and any(np.isclose(self.lower_left, upper_right)):
+            raise ValueError("mesh cannot have zero thickness is any dimension")
 
     @width.setter
     def width(self, width):
@@ -792,16 +792,6 @@ class RegularMesh(StructuredMesh):
             volume_normalization=volume_normalization
         )
 
-    def is_flat(self):
-        """Returns True if the mesh is flat
-        """
-        if self.lower_left is None or self.upper_right is None:
-            return False
-
-        for val1, val2 in zip(self.lower_left, self.upper_right):
-            if val1 == val2:
-                return True
-
 def Mesh(*args, **kwargs):
     warnings.warn("Mesh has been renamed RegularMesh. Future versions of "
                   "OpenMC will not accept the name Mesh.")
diff --git a/tests/unit_tests/test_mesh.py b/tests/unit_tests/test_mesh.py
index 8bc00a2768..0f9b96b0b3 100644
--- a/tests/unit_tests/test_mesh.py
+++ b/tests/unit_tests/test_mesh.py
@@ -33,25 +33,3 @@ def test_raises_error_when_flat(val_left, val_right):
     with pytest.raises(ValueError):
         mesh.upper_right = [25, 25, val_right]
         mesh.lower_left = [-25, -25, val_left]
-
-
-def test_corner_none_returns_false():
-    """Checks mesh is not considered flat when one
-    corner is None
-    """
-    mesh = openmc.RegularMesh()
-    mesh.lower_left = [-25, -25, -25]
-    assert not mesh.is_flat()
-
-    mesh = openmc.RegularMesh()
-    mesh.upper_right = [-25, -25, -25]
-    assert not mesh.is_flat()
-
-    # test with np array
-    mesh = openmc.RegularMesh()
-    mesh.lower_left = np.array([-25, -25, -25])
-    assert not mesh.is_flat()
-
-    mesh = openmc.RegularMesh()
-    mesh.upper_right = np.array([-25, -25, -25])
-    assert not mesh.is_flat()
\ No newline at end of file