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-rw-r--r--numpy/lib/function_base.py7
1 files changed, 5 insertions, 2 deletions
diff --git a/numpy/lib/function_base.py b/numpy/lib/function_base.py
index 9d380e67d..21532838b 100644
--- a/numpy/lib/function_base.py
+++ b/numpy/lib/function_base.py
@@ -316,14 +316,17 @@ def average(a, axis=None, weights=None, returned=False):
The weights array can either be 1-D (in which case its length must be
the size of `a` along the given axis) or of the same shape as `a`.
If `weights=None`, then all data in `a` are assumed to have a
- weight equal to one.
+ weight equal to one. The 1-D calculation is::
+
+ avg = sum(a * weights) / sum(weights)
+
+ The only constraint on `weights` is that `sum(weights)` must not be 0.
returned : bool, optional
Default is `False`. If `True`, the tuple (`average`, `sum_of_weights`)
is returned, otherwise only the average is returned.
If `weights=None`, `sum_of_weights` is equivalent to the number of
elements over which the average is taken.
-
Returns
-------
retval, [sum_of_weights] : array_type or double