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-rw-r--r--numpy/core/fromnumeric.py23
1 files changed, 12 insertions, 11 deletions
diff --git a/numpy/core/fromnumeric.py b/numpy/core/fromnumeric.py
index 285b75314..fa8941828 100644
--- a/numpy/core/fromnumeric.py
+++ b/numpy/core/fromnumeric.py
@@ -3436,17 +3436,18 @@ def std(a, axis=None, dtype=None, out=None, ddof=0, keepdims=np._NoValue):
Notes
-----
The standard deviation is the square root of the average of the squared
- deviations from the mean, i.e., ``std = sqrt(mean(abs(x - x.mean())**2))``.
-
- The average squared deviation is normally calculated as
- ``x.sum() / N``, where ``N = len(x)``. If, however, `ddof` is specified,
- the divisor ``N - ddof`` is used instead. In standard statistical
- practice, ``ddof=1`` provides an unbiased estimator of the variance
- of the infinite population. ``ddof=0`` provides a maximum likelihood
- estimate of the variance for normally distributed variables. The
- standard deviation computed in this function is the square root of
- the estimated variance, so even with ``ddof=1``, it will not be an
- unbiased estimate of the standard deviation per se.
+ deviations from the mean, i.e., ``std = sqrt(mean(x))``, where
+ ``x = abs(a - a.mean())**2``.
+
+ The average squared deviation is typically calculated as ``x.sum() / N``,
+ where ``N = len(x)``. If, however, `ddof` is specified, the divisor
+ ``N - ddof`` is used instead. In standard statistical practice, ``ddof=1``
+ provides an unbiased estimator of the variance of the infinite population.
+ ``ddof=0`` provides a maximum likelihood estimate of the variance for
+ normally distributed variables. The standard deviation computed in this
+ function is the square root of the estimated variance, so even with
+ ``ddof=1``, it will not be an unbiased estimate of the standard deviation
+ per se.
Note that, for complex numbers, `std` takes the absolute
value before squaring, so that the result is always real and nonnegative.