Add N-ary broadcasting operations. (#98)

This PR adds N-ary broadcasting operations (in preparation for where) and simplifies code for the N-ary case.

Author: hameerabbasi

docs/generated/sparse.COO.elemwise.rst

@@ -31,7 +31,6 @@ COO
    .. autosummary::
       :toctree:
 
-      COO.elemwise
       COO.astype
       COO.round
 

docs/generated/sparse.COO.rst

@@ -0,0 +1,6 @@
+elemwise
+========
+
+.. currentmodule:: sparse
+
+.. autofunction:: elemwise

docs/generated/sparse.elemwise.rst

@@ -27,6 +27,8 @@ API
 
     dot
 
+    elemwise
+
     random
 
     stack

docs/generated/sparse.rst

@@ -33,16 +33,20 @@ or numpy functions that are not yet implemented for sparse arrays
 
 This page describes those valid operations, and their limitations.
 
-:obj:`COO.elemwise`
+:obj:`elemwise`
 ~~~~~~~~~~~~~~~~~~~
 This function allows you to apply any arbitrary unary or binary function where
 the first object is :obj:`COO`, and the second is a scalar, :obj:`COO`, or
-a :doc:`Numpy arrays <reference/generated/numpy.ndarray>`. For example, the
+a :obj:`scipy.sparse.spmatrix`. For example, the
 following will add two :obj:`COO` objects:
 
 .. code-block:: python
 
-   x.elemwise(np.add, y)
+   sparse.elemwise(np.add, x, y)
+
+
+.. note:: Previously, :obj:`elemwise` was a method of the :obj:`COO` class. Now,
+   it has been moved to the :obj:`sparse` module.
 
 .. _operations-auto-densification:
 
@@ -78,26 +82,8 @@ If densification is needed, it must be explicit. In other words, you must call
 :obj:`COO.todense` on the :obj:`COO` object. If both operands are :obj:`COO`,
 both must be densified.
 
-
-Operations with :doc:`Numpy arrays <reference/generated/numpy.ndarray>`
------------------------------------------------------------------------
-Certain operations with :obj:`numpy.ndarray` are also supported. For example,
-the following are all allowed if :code:`x` is a :obj:`numpy.ndarray` and
-:code:`(x == 0).all()` evaluates to :code:`True`:
-
-.. code-block:: python
-
-   x + y
-   x - y
-
-The following is true so long as there are no infinities or NaNs in :code:`x`:
-
-.. code-block:: python
-
-   x * y
-
-In general, if operating on the :code:`numpy.ndarray` with a zero would produce
-all-zeros then the operation is supported.
+.. note:: Previously, operations with Numpy arrays were sometimes supported. Now,
+   it is necessary to convert Numpy arrays to :obj:`COO` objects.
 
 
 Operations with :obj:`scipy.sparse.spmatrix`

docs/operations.rst

@@ -1,4 +1,4 @@
-from .coo import COO, tensordot, concatenate, stack, dot, triu, tril
+from .coo import COO, elemwise, tensordot, concatenate, stack, dot, triu, tril
 from .dok import DOK
 from .sparse_array import SparseArray
 from .utils import random