revert backends experiment

Author: ntessore

README.md

@@ -1,11 +1,9 @@
-
-transformcl
-===========
+# transformcl
 
 **Transform angular power spectra and correlation functions.**
 
 This is a minimal Python package for transformations between angular power
-spectra and correlation functions.  It is currently limited to the spin zero
+spectra and correlation functions. It is currently limited to the spin zero
 case.
 
 The package can be installed using pip:
@@ -22,30 +20,7 @@ ct = transformcl.corr(cl)
 
 For more information, please see the [documentation].
 
-Current functionality covers the absolutely minimal use case.  Please open an
+Current functionality covers the absolutely minimal use case. Please open an
 issue on GitHub if you would like to see anything added.
 
 [documentation]: https://glass.readthedocs.io/projects/transformcl/latest
-
-
-Backends
---------
-The `transformcl` package supports multiple transform backends.  The
-current backend can be changed globally by assigning to
-`transformcl.backend`:
-
-```py
-transformcl.backend = "<choice>"
-...
-```
-
-or using the `transformcl.use()` context manager:
-
-```py
-with transformcl.use("<choice>"):
-    ...
-```
-
-The list of available backends can be found in the [documentation][backends].
-
-[backends]: https://glass.readthedocs.io/projects/transformcl/latest#backends

docs/index.rst

@@ -19,53 +19,10 @@ Current functionality covers the absolutely minimal use case.  Please open an
 issue on GitHub if you would like to see anything added.
 
 
-.. _backends:
-
-Backends
---------
-The :mod:`transformcl` module supports multiple transform backends.  The
-current backend can be changed globally by assigning to
-:data:`transformcl.backend`::
-
-    transformcl.backend = "<choice>"
-    ...
-
-or using the :func:`transformcl.use` context manager::
-
-    with transformcl.use("<choice>"):
-        ...
-
-The following backends are available:
-
-.. data:: transformcl.backend
-   :value: "flt-ii"
-   :no-index:
-
-   The "open" Discrete Legendre Transform (DLT) as implemented by the
-   :doc:`flt:index` package, with correlation function values over the open
-   interval :math:`(0, \pi)`.
-
-   .. note:: This is the default backend. It supports multiple array types.
-
-.. data:: transformcl.backend
-   :value: "flt-i"
-   :no-index:
-
-   The "closed" Discrete Legendre Transform (DLT) as implemented by the
-   :doc:`flt:index` package, with correlation function values over the closed
-   interval :math:`[0, \pi]`.
-
-   .. caution:: This transform should be used with care.  The correlation
-      function values are computed all the way to :math:`\theta = 0` from a
-      finite bandlimited angular power spectrum.
-
-
 Reference
 ---------
 
-.. autodata:: transformcl.backend
-.. autofunction:: transformcl.use
-.. autofunction:: transformcl.theta
 .. autofunction:: transformcl.corr
 .. autofunction:: transformcl.cl
 .. autofunction:: transformcl.var
+.. autofunction:: transformcl.theta

transformcl.py

@@ -1,56 +1,37 @@
 """Transform angular power spectra."""
 
 __all__ = [
-    "backend",
     "cl",
     "corr",
     "theta",
-    "use",
     "var",
 ]
 
-from contextlib import contextmanager
-from typing import Literal
-
 from array_api_compat import array_namespace
 
-BackendStr = Literal[
-    "flt-ii",
-    "flt-i",
-]
-
-
-backend: BackendStr = "flt-ii"
-"""Backend for transforms. See :ref:`backends`."""
-
-
-@contextmanager
-def use(choice: BackendStr) -> None:
-    """Context manager to change backend. See :ref:`backends`."""
-    global backend
-    restore = backend
-    backend = choice
-    try:
-        yield
-    finally:
-        backend = restore
+import flt
 
 
-def corr(cl):
+def corr(cl, closed=False):
     r"""
     Transform angular power spectrum to angular correlation function.
 
     Takes an angular power spectrum with :math:`\mathtt{n} =
     \mathtt{lmax}+1` coefficients and returns the corresponding angular
     correlation function in :math:`\mathtt{n}` points.
 
-    The correlation function is computed at the angles returned by
-    :func:`transformcl.theta`.
+    The correlation function values can be computed either over the
+    closed interval :math:`[0, \pi]`, in which case :math:`\theta_0 = 0`
+    and :math:`\theta_{n-1} = \pi`, or over the open interval :math:`(0,
+    \pi)`.
 
     Parameters
     ----------
     cl : (n,) array_like
         Angular power spectrum from :math:`0` to :math:`\mathtt{lmax}`.
+    closed : bool
+        Compute correlation function over open (``closed=False``) or closed
+        (``closed=True``) interval.
 
     Returns
     -------
@@ -66,30 +47,20 @@ def corr(cl):
 
     """
 
+    xp = array_namespace(cl)
+
     # length n of the transform
     if cl.ndim != 1:
         raise TypeError("cl must be 1d array")
     n = cl.shape[-1]
 
-    if backend in ["flt-ii", "flt-i"]:
-        xp = array_namespace(cl)
-        # DLT coefficients = (2l+1)/(4pi) * Cl
-        a = (2 * xp.arange(n) + 1) / (4 * xp.pi) * cl
-
-        if backend == "flt-ii":
-            import flt
-
-            return flt.idlt(a)
-
-        if backend == "flt-i":
-            import flt
+    # DLT coefficients = (2l+1)/(4pi) * Cl
+    a = (2 * xp.arange(n) + 1) / (4 * xp.pi) * cl
 
-            return flt.idlt(a, True)
+    return flt.idlt(a, closed)
 
-    raise NotImplementedError(f"unknown backend {backend!r}")
 
-
-def cl(corr):
+def cl(corr, closed=False):
     r"""
     Transform angular correlation function to angular power spectrum.
 
@@ -98,7 +69,10 @@ def cl(corr):
     :math:`\mathtt{lmax} = \mathtt{n}-1`.
 
     The correlation function must be given at the angles returned by
-    :func:`transformcl.theta`.
+    :func:`transformcl.theta`.  These can be distributed either over the
+    closed interval :math:`[0, \pi]`, in which case :math:`\theta_0 = 0`
+    and :math:`\theta_{n-1} = \pi`, or over the open interval :math:`(0,
+    \pi)`.
 
     Parameters
     ----------
@@ -109,6 +83,9 @@ def cl(corr):
     -------
     cl : (n,) array_like
         Angular power spectrum from :math:`0` to :math:`\mathtt{lmax}`.
+    closed : bool
+        Compute correlation function over open (``closed=False``) or
+        closed (``closed=True``) interval.
 
     See Also
     --------
@@ -119,27 +96,17 @@ def cl(corr):
 
     """
 
+    xp = array_namespace(corr)
+
     # length n of the transform
     if corr.ndim != 1:
         raise TypeError("corr must be 1d array")
     n = corr.shape[-1]
 
-    if backend in ["flt-ii", "flt-i"]:
-        xp = array_namespace(corr)
-        # DLT coefficients = (2l+1)/(4pi) * Cl
-        fl = (2 * xp.arange(n) + 1) / (4 * xp.pi)
-
-        if backend == "flt-ii":
-            import flt
-
-            return flt.dlt(corr) / fl
-
-        if backend == "flt-i":
-            import flt
+    # DLT coefficients = (2l+1)/(4pi) * Cl
+    fl = (2 * xp.arange(n) + 1) / (4 * xp.pi)
 
-            return flt.dlt(corr, True) / fl
-
-    raise NotImplementedError(f"unknown backend {backend!r}")
+    return flt.dlt(corr, closed) / fl
 
 
 def var(cl):
@@ -175,22 +142,12 @@ def var(cl):
     return xp.sum((2 * ell + 1) / (4 * xp.pi) * cl, axis=-1)
 
 
-def theta(n):
+def theta(n, closed=False):
     r"""
     Return the angles :math:`\theta_1, \ldots, \theta_n` of the
     correlation function with *n* points.
     """
-
-    if backend == "flt-ii":
-        import flt
-
-        return flt.theta(n)
-    if backend == "flt-i":
-        import flt
-
-        return flt.theta(n, True)
-
-    raise NotImplementedError(f"unknown backend {backend!r}")
+    return flt.theta(n, closed)
 
 
 cltocorr = corr