ENH: delegate sinc function.

Author: Enderdead

src/array_api_extra/__init__.py

@@ -1,6 +1,6 @@
 """Extra array functions built on top of the array API standard."""
 
-from ._delegation import expand_dims, isclose, nan_to_num, one_hot, pad
+from ._delegation import expand_dims, isclose, nan_to_num, one_hot, pad, sinc
 from ._lib._at import at
 from ._lib._funcs import (
     apply_where,
@@ -12,7 +12,6 @@
     kron,
     nunique,
     setdiff1d,
-    sinc,
 )
 from ._lib._lazy import lazy_apply
 

src/array_api_extra/_delegation.py

@@ -18,7 +18,7 @@
 from ._lib._utils._helpers import asarrays
 from ._lib._utils._typing import Array, DType
 
-__all__ = ["expand_dims", "isclose", "nan_to_num", "one_hot", "pad"]
+__all__ = ["expand_dims", "isclose", "nan_to_num", "one_hot", "pad", "sinc"]
 
 
 def expand_dims(
@@ -414,3 +414,97 @@ def pad(
         return xp.nn.functional.pad(x, tuple(pad_width), value=constant_values)  # type: ignore[arg-type]  # pyright: ignore[reportArgumentType]
 
     return _funcs.pad(x, pad_width, constant_values=constant_values, xp=xp)
+
+
+def sinc(x: Array, /, *, xp: ModuleType | None = None) -> Array:
+    r"""
+    Return the normalized sinc function.
+
+    The sinc function is equal to :math:`\sin(\pi x)/(\pi x)` for any argument
+    :math:`x\ne 0`. ``sinc(0)`` takes the limit value 1, making ``sinc`` not
+    only everywhere continuous but also infinitely differentiable.
+
+    .. note::
+
+        Note the normalization factor of ``pi`` used in the definition.
+        This is the most commonly used definition in signal processing.
+        Use ``sinc(x / xp.pi)`` to obtain the unnormalized sinc function
+        :math:`\sin(x)/x` that is more common in mathematics.
+
+    Parameters
+    ----------
+    x : array
+        Array (possibly multi-dimensional) of values for which to calculate
+        ``sinc(x)``. Must have a real floating point dtype.
+    xp : array_namespace, optional
+        The standard-compatible namespace for `x`. Default: infer.
+
+    Returns
+    -------
+    array
+        ``sinc(x)`` calculated elementwise, which has the same shape as the input.
+
+    Notes
+    -----
+    The name sinc is short for "sine cardinal" or "sinus cardinalis".
+
+    The sinc function is used in various signal processing applications,
+    including in anti-aliasing, in the construction of a Lanczos resampling
+    filter, and in interpolation.
+
+    For bandlimited interpolation of discrete-time signals, the ideal
+    interpolation kernel is proportional to the sinc function.
+
+    References
+    ----------
+    #. Weisstein, Eric W. "Sinc Function." From MathWorld--A Wolfram Web
+       Resource. https://mathworld.wolfram.com/SincFunction.html
+    #. Wikipedia, "Sinc function",
+       https://en.wikipedia.org/wiki/Sinc_function
+
+    Examples
+    --------
+    >>> import array_api_strict as xp
+    >>> import array_api_extra as xpx
+    >>> x = xp.linspace(-4, 4, 41)
+    >>> xpx.sinc(x, xp=xp)
+    Array([-3.89817183e-17, -4.92362781e-02,
+           -8.40918587e-02, -8.90384387e-02,
+           -5.84680802e-02,  3.89817183e-17,
+            6.68206631e-02,  1.16434881e-01,
+            1.26137788e-01,  8.50444803e-02,
+           -3.89817183e-17, -1.03943254e-01,
+           -1.89206682e-01, -2.16236208e-01,
+           -1.55914881e-01,  3.89817183e-17,
+            2.33872321e-01,  5.04551152e-01,
+            7.56826729e-01,  9.35489284e-01,
+            1.00000000e+00,  9.35489284e-01,
+            7.56826729e-01,  5.04551152e-01,
+            2.33872321e-01,  3.89817183e-17,
+           -1.55914881e-01, -2.16236208e-01,
+           -1.89206682e-01, -1.03943254e-01,
+           -3.89817183e-17,  8.50444803e-02,
+            1.26137788e-01,  1.16434881e-01,
+            6.68206631e-02,  3.89817183e-17,
+           -5.84680802e-02, -8.90384387e-02,
+           -8.40918587e-02, -4.92362781e-02,
+           -3.89817183e-17], dtype=array_api_strict.float64)
+    """
+
+    if xp is None:
+        xp = array_namespace(x)
+
+    if not xp.isdtype(x.dtype, "real floating"):
+        err_msg = "`x` must have a real floating data type."
+        raise ValueError(err_msg)
+
+    if (
+        is_numpy_namespace(xp)
+        or is_cupy_namespace(xp)
+        or is_jax_namespace(xp)
+        or is_torch_namespace(xp)
+        or is_dask_namespace(xp)
+    ):
+        return xp.sinc(x)
+
+    return _funcs.sinc(x, xp=xp)

src/array_api_extra/_lib/_funcs.py

@@ -864,86 +864,10 @@ def setdiff1d(
     return x1_[_helpers.in1d(x1_, x2_, assume_unique=True, invert=True, xp=xp)]
 
 
-def sinc(x: Array, /, *, xp: ModuleType | None = None) -> Array:
-    r"""
-    Return the normalized sinc function.
-
-    The sinc function is equal to :math:`\sin(\pi x)/(\pi x)` for any argument
-    :math:`x\ne 0`. ``sinc(0)`` takes the limit value 1, making ``sinc`` not
-    only everywhere continuous but also infinitely differentiable.
-
-    .. note::
-
-        Note the normalization factor of ``pi`` used in the definition.
-        This is the most commonly used definition in signal processing.
-        Use ``sinc(x / xp.pi)`` to obtain the unnormalized sinc function
-        :math:`\sin(x)/x` that is more common in mathematics.
-
-    Parameters
-    ----------
-    x : array
-        Array (possibly multi-dimensional) of values for which to calculate
-        ``sinc(x)``. Must have a real floating point dtype.
-    xp : array_namespace, optional
-        The standard-compatible namespace for `x`. Default: infer.
-
-    Returns
-    -------
-    array
-        ``sinc(x)`` calculated elementwise, which has the same shape as the input.
-
-    Notes
-    -----
-    The name sinc is short for "sine cardinal" or "sinus cardinalis".
-
-    The sinc function is used in various signal processing applications,
-    including in anti-aliasing, in the construction of a Lanczos resampling
-    filter, and in interpolation.
-
-    For bandlimited interpolation of discrete-time signals, the ideal
-    interpolation kernel is proportional to the sinc function.
-
-    References
-    ----------
-    #. Weisstein, Eric W. "Sinc Function." From MathWorld--A Wolfram Web
-       Resource. https://mathworld.wolfram.com/SincFunction.html
-    #. Wikipedia, "Sinc function",
-       https://en.wikipedia.org/wiki/Sinc_function
-
-    Examples
-    --------
-    >>> import array_api_strict as xp
-    >>> import array_api_extra as xpx
-    >>> x = xp.linspace(-4, 4, 41)
-    >>> xpx.sinc(x, xp=xp)
-    Array([-3.89817183e-17, -4.92362781e-02,
-           -8.40918587e-02, -8.90384387e-02,
-           -5.84680802e-02,  3.89817183e-17,
-            6.68206631e-02,  1.16434881e-01,
-            1.26137788e-01,  8.50444803e-02,
-           -3.89817183e-17, -1.03943254e-01,
-           -1.89206682e-01, -2.16236208e-01,
-           -1.55914881e-01,  3.89817183e-17,
-            2.33872321e-01,  5.04551152e-01,
-            7.56826729e-01,  9.35489284e-01,
-            1.00000000e+00,  9.35489284e-01,
-            7.56826729e-01,  5.04551152e-01,
-            2.33872321e-01,  3.89817183e-17,
-           -1.55914881e-01, -2.16236208e-01,
-           -1.89206682e-01, -1.03943254e-01,
-           -3.89817183e-17,  8.50444803e-02,
-            1.26137788e-01,  1.16434881e-01,
-            6.68206631e-02,  3.89817183e-17,
-           -5.84680802e-02, -8.90384387e-02,
-           -8.40918587e-02, -4.92362781e-02,
-           -3.89817183e-17], dtype=array_api_strict.float64)
-    """
-    if xp is None:
-        xp = array_namespace(x)
+def sinc(x: Array, /, *, xp: ModuleType) -> Array:
+    # numpydoc ignore=PR01,RT01
+    """See docstring in `array_api_extra._delegation.py`."""
 
-    if not xp.isdtype(x.dtype, "real floating"):
-        err_msg = "`x` must have a real floating data type."
-        raise ValueError(err_msg)
     # no scalars in `where` - array-api#807
     y = xp.pi * xp.where(
         xp.astype(x, xp.bool),