Add 2d checkered pattern

mbuild/pattern.py

@@ -15,6 +15,7 @@
     "Random3DPattern",
     "Grid2DPattern",
     "Grid3DPattern",
+    "Checkered2DPattern",
 ]
 
 
@@ -274,6 +275,48 @@ def __init__(self, n, m, l, **kwargs):
         super(Grid3DPattern, self).__init__(points=points, **kwargs)
 
 
+class Checkered2DPattern(Pattern):
+    """Generate a 2D grid (n x m) of points along z = 0.
+
+    Notes
+    -----
+    Points span [0,1) along x and y axes
+
+    Attributes
+    ----------
+    n : int
+        Number of grid rows
+    m : int
+        Number of grid columns
+    shift : str, optional, default="column"
+        Allow user to choose the pattern to be shifted by "column" or "row"
+    """
+
+    def __init__(self, n, m, shift="column", **kwargs):
+        points = np.zeros(shape=(n * m, 3), dtype=float)
+        if shift == "row":
+            for i, j in product(range(n), range(m)):
+                if i % 2 == 0:
+                    points[i * m + j, 0] = i / n
+                    points[i * m + j, 1] = j / m
+                else:
+                    points[i * m + j, 0] = i / n
+                    points[i * m + j, 1] = j / m + (1 / (2 * m))
+        elif shift == "column":
+            for i, j in product(range(n), range(m)):
+                if j % 2 == 0:
+                    points[i * m + j, 0] = i / n
+                    points[i * m + j, 1] = j / m
+                else:
+                    points[i * m + j, 0] = i / n + (1 / (2 * n))
+                    points[i * m + j, 1] = j / m
+        else:
+            raise ValueError(
+                f"shift can only take value of 'column' or 'row', given {shift}"
+            )
+        super(Checkered2DPattern, self).__init__(points=points, **kwargs)
+
+
 class SpherePattern(Pattern):
     """Generate N evenly distributed points on the unit sphere.
 

mbuild/tests/test_pattern.py

@@ -56,6 +56,16 @@ def test_grid_3d(self):
         pattern = mb.Grid3DPattern(10, 5, 2)
         assert len(pattern) == 100
 
+    def test_checkered_2d(self):
+        pattern = mb.Checkered2DPattern(10, 5)
+        assert len(pattern) == 50
+
+        pattern = mb.Checkered2DPattern(5, 5, "row")
+        assert len(pattern) == 25
+
+        with pytest.raises(ValueError):
+            pattern = mb.Checkered2DPattern(5, 5, "bogus")
+
     def test_sphere(self):
         pattern = mb.SpherePattern(100)
         assert len(pattern) == 100