Fix create_pixel_dim (#567)

Co-authored-by: Walter Simson <walter.a.simson@gmail.com>

Author: faridyagubbayli

kwave/utils/mapgen.py

@@ -935,7 +935,7 @@ def create_pixel_dim(Nx: int, origin_size: float, shift: float) -> Tuple[np.ndar
 
         # pixel numbering has a double centre point
         else:
-            nx = np.hstack([np.arange(-Nx / 2 + 1, 0 + 1, 1), np.arange(0, -Nx / 2 - 1 + 1, 1)])
+            nx = np.hstack([np.arange(-Nx / 2 + 1, 0 + 1, 1), np.arange(0, Nx / 2 - 1 + 1, 1)])
 
     # grid dimension has an odd number of points
     else:

tests/test_create_pixel_dim.py

@@ -0,0 +1,64 @@
+import pytest
+import numpy as np
+
+from kwave.utils.mapgen import create_pixel_dim
+
+
+def test_even_single_shift0():
+    Nx = 4
+    origin_size = "single"
+    shift = 0
+
+    result = create_pixel_dim(Nx, origin_size, shift)
+    expected = np.array([-1, 0, 1, 2])  # from the code path
+    np.testing.assert_array_equal(result, expected)
+
+
+def test_even_single_shift1():
+    Nx = 4
+    origin_size = "single"
+    shift = 1
+
+    result = create_pixel_dim(Nx, origin_size, shift)
+    expected = np.array([-2, -1, 0, 1])  # from code path
+    np.testing.assert_array_equal(result, expected)
+
+
+def test_even_double_shift_any():
+    Nx = 4
+    origin_size = "double"
+    shift = 999  # any shift, code doesn't branch on shift for Nx even
+
+    result = create_pixel_dim(Nx, origin_size, shift)
+    expected = np.array([-1, 0, 0, 1])  # based on code as-is
+    np.testing.assert_array_equal(result, expected)
+
+
+def test_odd_single():
+    Nx = 5
+    origin_size = "single"
+    shift = 0  # or shift=1 doesn't matter for this branch
+
+    result = create_pixel_dim(Nx, origin_size, shift)
+    expected = np.array([-2, -1, 0, 1, 2])
+    np.testing.assert_array_equal(result, expected)
+
+
+def test_odd_double_shift0():
+    Nx = 5
+    origin_size = "double"
+    shift = 0
+
+    result = create_pixel_dim(Nx, origin_size, shift)
+    expected = np.array([-1, 0, 0, 1, 2])  # consistent with code
+    np.testing.assert_array_equal(result, expected)
+
+
+def test_odd_double_shift1():
+    Nx = 5
+    origin_size = "double"
+    shift = 1
+
+    result = create_pixel_dim(Nx, origin_size, shift)
+    expected = np.array([-2, -1, 0, 0, 1])
+    np.testing.assert_array_equal(result, expected)