Merge pull request #54 from scipp/define-chopper-widths-centers

Allow to create choppers from centers and widths of cutouts

src/tof/chopper.py

@@ -29,10 +29,6 @@ class Chopper:
     ----------
     frequency:
         The frequency of the chopper. Must be positive.
-    open:
-        The opening angles of the chopper cutouts.
-    close:
-        The closing angles of the chopper cutouts.
     distance:
         The distance from the source to the chopper.
     phase:
@@ -41,17 +37,32 @@ class Chopper:
         to the chopper rotation direction. For example, if the chopper rotates
         clockwise, a phase of 10 degrees will shift all window angles by 10 degrees
         in the anticlockwise direction, which will result in the windows opening later.
+    open:
+        The opening angles of the chopper cutouts.
+    close:
+        The closing angles of the chopper cutouts.
+    centers:
+        The centers of the chopper cutouts.
+    widths:
+        The widths of the chopper cutouts.
     name:
         The name of the chopper.
+
+    Notes
+    -----
+    Either `open` and `close` or `centers` and `widths` must be provided, but not both.
     """
 
     def __init__(
         self,
+        *,
         frequency: sc.Variable,
-        open: sc.Variable,
-        close: sc.Variable,
         distance: sc.Variable,
         phase: sc.Variable,
+        open: sc.Variable | None = None,
+        close: sc.Variable | None = None,
+        centers: sc.Variable | None = None,
+        widths: sc.Variable | None = None,
         direction: Direction = Clockwise,
         name: str = "",
     ):
@@ -64,6 +75,20 @@ def __init__(
                 f", got {direction}."
             )
         self.direction = direction
+        # Check that either open/close or centers/widths are provided, but not both
+        if tuple(x for x in (open, close, centers, widths) if x is not None) not in (
+            (open, close),
+            (centers, widths),
+        ):
+            raise ValueError(
+                "Either open/close or centers/widths must be provided, got"
+                f" open={open}, close={close}, centers={centers}, widths={widths}."
+            )
+        if open is None:
+            half_width = widths * 0.5
+            open = centers - half_width
+            close = centers + half_width
+
         self.open = (open if open.dims else open.flatten(to='cutout')).to(
             dtype=float, copy=False
         )

tests/chopper_test.py

@@ -291,3 +291,43 @@ def test_bad_direction_raises():
             distance=d,
             direction=1,
         )
+
+
+def test_chopper_create_from_centers_and_widths():
+    f = 10.0 * Hz
+    centers = sc.array(dims=['cutout'], values=[15.0, 46.0], unit='deg')
+    widths = sc.array(dims=['cutout'], values=[10.0, 16.0], unit='deg')
+    chopper = tof.Chopper(
+        frequency=f,
+        centers=centers,
+        widths=widths,
+        phase=0.0 * deg,
+        distance=5.0 * meter,
+    )
+    assert sc.allclose(chopper.open, centers - widths / 2)
+    assert sc.allclose(chopper.close, centers + widths / 2)
+
+    expected = tof.Chopper(
+        frequency=f,
+        open=sc.array(dims=['cutout'], values=[10.0, 38.0], unit='deg'),
+        close=sc.array(dims=['cutout'], values=[20.0, 54.0], unit='deg'),
+        phase=0.0 * deg,
+        distance=5.0 * meter,
+    )
+    assert sc.allclose(chopper.open, expected.open)
+    assert sc.allclose(chopper.close, expected.close)
+
+
+def test_chopper_create_raises_when_both_edges_and_centers_are_supplied():
+    with pytest.raises(
+        ValueError, match="Either open/close or centers/widths must be provided"
+    ):
+        tof.Chopper(
+            frequency=10.0 * Hz,
+            open=10.0 * deg,
+            close=20.0 * deg,
+            centers=15.0 * deg,
+            widths=10.0 * deg,
+            phase=0.0 * deg,
+            distance=5.0 * meter,
+        )