Added note to prefix documentation for corner cases where cunumeric r…

…esults can diverge from numpy (nv-legate#528)

* Added note to prefix documentation for corner cases where cunumeric results can diverge from numpy. Also other minor fixes to prefix documentation.

* Minor changes to documentation phrasing.

cunumeric/module.py

@@ -4654,13 +4654,13 @@ def cumprod(
         Input array.
 
     axis : int, optional
-        Axis along which the cumulative sum is computed. The default (None) is
-        to compute the cumsum over the flattened array.
+        Axis along which the cumulative product is computed. The default (None)
+        is to compute the cumprod over the flattened array.
 
     dtype : dtype, optional
         Type of the returned array and of the accumulator in which the elements
-        are summed. If dtype is not specified, it defaults to the dtype of a,
-        unless a has an integer dtype with a precision less than that of the
+        are multiplied. If dtype is not specified, it defaults to the dtype of
+        a, unless a has an integer dtype with a precision less than that of the
         default platform integer. In that case, the default platform integer is
         used.
     out : ndarray, optional
@@ -4670,7 +4670,7 @@ def cumprod(
 
     Returns
     -------
-    cumprod_along_axis : ndarray.
+    cumprod : ndarray
         A new array holding the result is returned unless out is specified, in
         which case a reference to out is returned. The result has the same size
         as a, and the same shape as a if axis is not None or a is a 1-d array.
@@ -4679,6 +4679,16 @@ def cumprod(
     --------
     numpy.cumprod
 
+    Notes
+    -----
+    CuNumeric's parallel implementation may yield different results from NumPy
+    with floating point and complex types. For example, when boundary values
+    such as inf occur they may not propagate as expected. Consider the float32
+    array ``[3e+37, 1, 100, 0.01]``. NumPy's cumprod will return a result of
+    ``[3e+37, 3e+37, inf, inf]``. However, cuNumeric might internally partition
+    the array such that partition 0 has ``[3e+37, 1]``  and partition 1 has
+    ``[100, 0.01]``, returning the result ``[3e+37, 3e+37, inf, 3e+37]``.
+
     Availability
     --------
     Multiple GPUs, Multiple CPUs
@@ -4725,7 +4735,7 @@ def cumsum(
 
     Returns
     -------
-    cumsum_along_axis : ndarray.
+    cumsum : ndarray.
         A new array holding the result is returned unless out is specified, in
         which case a reference to out is returned. The result has the same size
         as a, and the same shape as a if axis is not None or a is a 1-d array.
@@ -4734,6 +4744,13 @@ def cumsum(
     --------
     numpy.cumsum
 
+    Notes
+    -----
+    CuNumeric's parallel implementation may yield different results from NumPy
+    with floating point and complex types. For example, when boundary values
+    such as inf occur they may not propagate as expected. For more explanation
+    check cunumeric.cumprod.
+
     Availability
     --------
     Multiple GPUs, Multiple CPUs
@@ -4763,13 +4780,13 @@ def nancumprod(
         Input array.
 
     axis : int, optional
-        Axis along which the cumulative sum is computed. The default (None) is
-        to compute the cumsum over the flattened array.
+        Axis along which the cumulative product is computed. The default (None)
+        is to compute the nancumprod over the flattened array.
 
     dtype : dtype, optional
         Type of the returned array and of the accumulator in which the elements
-        are summed. If dtype is not specified, it defaults to the dtype of a,
-        unless a has an integer dtype with a precision less than that of the
+        are multiplied. If dtype is not specified, it defaults to the dtype of
+        a, unless a has an integer dtype with a precision less than that of the
         default platform integer. In that case, the default platform integer is
         used.
     out : ndarray, optional
@@ -4779,7 +4796,7 @@ def nancumprod(
 
     Returns
     -------
-    cumprod_along_axis : ndarray.
+    nancumprod : ndarray.
         A new array holding the result is returned unless out is specified, in
         which case a reference to out is returned. The result has the same size
         as a, and the same shape as a if axis is not None or a is a 1-d array.
@@ -4788,6 +4805,13 @@ def nancumprod(
     --------
     numpy.nancumprod
 
+    Notes
+    -----
+    CuNumeric's parallel implementation may yield different results from NumPy
+    with floating point and complex types. For example, when boundary values
+    such as inf occur they may not propagate as expected. For more explanation
+    check cunumeric.cumprod.
+
     Availability
     --------
     Multiple GPUs, Multiple CPUs
@@ -4818,7 +4842,7 @@ def nancumsum(
 
     axis : int, optional
         Axis along which the cumulative sum is computed. The default (None) is
-        to compute the cumsum over the flattened array.
+        to compute the nancumsum over the flattened array.
 
     dtype : dtype, optional
         Type of the returned array and of the accumulator in which the elements
@@ -4833,7 +4857,7 @@ def nancumsum(
 
     Returns
     -------
-    cumsum_along_axis : ndarray.
+    nancumsum : ndarray.
         A new array holding the result is returned unless out is specified, in
         which case a reference to out is returned. The result has the same size
         as a, and the same shape as a if axis is not None or a is a 1-d array.
@@ -4842,6 +4866,13 @@ def nancumsum(
     --------
     numpy.nancumsum
 
+    Notes
+    -----
+    CuNumeric's parallel implementation may yield different results from NumPy
+    with floating point and complex types. For example, when boundary values
+    such as inf occur they may not propagate as expected. For more explanation
+    check cunumeric.cumprod.
+
     Availability
     --------
     Multiple GPUs, Multiple CPUs