ENH: add angle

src/array_api_extra/__init__.py

@@ -19,6 +19,7 @@
 )
 from ._lib._at import at
 from ._lib._funcs import (
+    angle,
     apply_where,
     broadcast_shapes,
     default_dtype,
@@ -32,6 +33,7 @@
 # pylint: disable=duplicate-code
 __all__ = [
     "__version__",
+    "angle",
     "apply_where",
     "argpartition",
     "at",

src/array_api_extra/_lib/_funcs.py

@@ -818,3 +818,36 @@ def union1d(a: Array, b: Array, /, *, xp: ModuleType) -> Array:
     b = xp.reshape(b, (-1,))
     # XXX: `sparse` returns NumPy arrays from `unique_values`
     return xp.asarray(xp.unique_values(xp.concat([a, b])))
+
+
+def angle(z: Array, deg: bool = False, /, *, xp: ModuleType | None = None) -> Array:
+    """
+    Return the angle of the complex argument.
+
+    Parameters
+    ----------
+    z : Array
+        Input array.
+    deg : bool, optional
+        Return angle in degrees if True, radians if False (default).
+    xp : array_namespace, optional
+        The standard-compatible namespace for `z`. Default: infer.
+
+    Returns
+    -------
+    ndarray or scalar
+        The counterclockwise angle from the positive real axis on the complex
+        plane in the range ``(-pi, pi]``, with dtype as float64.
+    """
+    if xp is None:
+        xp = array_namespace(z)
+    if xp.isdtype(z.dtype, "complex floating"):
+        zimage = xp.imag(z)
+        zreal = xp.real(z)
+    else:
+        zimage = xp.zeros_like(z, dtype=xp.float64)
+        zreal = xp.astype(z, xp.float64)
+    a = xp.atan2(zimage, zreal)
+    if deg:
+        a = a * 180 / xp.pi
+    return a

tests/test_funcs.py

@@ -13,6 +13,7 @@
 from typing_extensions import override
 
 from array_api_extra import (
+    angle,
     apply_where,
     argpartition,
     at,
@@ -1881,3 +1882,30 @@ def test_device(self, xp: ModuleType, device: Device):
         a = xp.asarray([-1, 1, 0], device=device)
         b = xp.asarray([2, -2, 0], device=device)
         assert get_device(union1d(a, b)) == device
+
+
+class TestAngle:
+    def test_simple(self, xp: ModuleType):
+        a = xp.asarray([1, 0])
+        expected = xp.asarray([0.0, 0.0], dtype=xp.float64)
+        res = angle(a)
+        xp_assert_equal(res, expected)
+
+    def test_complex(self, xp: ModuleType):
+        a = xp.asarray([1 + 1j, 1 - 1j, -1 + 1j, -1 - 1j])
+        expected = xp.asarray([np.pi / 4, -np.pi / 4, 3 * np.pi / 4, -3 * np.pi / 4])
+        res = angle(a)
+        xp_assert_equal(res, expected)
+
+    def test_2d(self, xp: ModuleType):
+        a = xp.asarray([[1 + 1j, 1 - 1j], [-1 + 1j, -1 - 1j]])
+        expected = xp.asarray(
+            [[np.pi / 4, -np.pi / 4], [3 * np.pi / 4, -3 * np.pi / 4]]
+        )
+        res = angle(a)
+        xp_assert_equal(res, expected)
+
+    @pytest.mark.skip_xp_backend(Backend.TORCH, reason="materialize 'meta' device")
+    def test_device(self, xp: ModuleType, device: Device):
+        a = xp.asarray([1 + 1j], device=device)
+        assert get_device(angle(a)) == device