Merge pull request #7470 from dstansby/correlation-docstrings

tacaswell · web-flow · commit 258dbf5c4086 · 2016-11-19T23:34:01.000-05:00
DOC: Clarify cross correlation documentation #1835
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -1673,8 +1673,7 @@ def acorr(self, x, **kwargs):
             normalization.
 
         normed : boolean, optional, default: True
-            if True, normalize the data by the autocorrelation at the 0-th
-            lag.
+            if True, input vectors are normalised to unit length.
 
         usevlines : boolean, optional, default: True
             if True, Axes.vlines is used to plot the vertical lines from the
@@ -1723,6 +1722,8 @@ def xcorr(self, x, y, normed=True, detrend=mlab.detrend_none,
         """
         Plot the cross correlation between *x* and *y*.
 
+        The correlation with lag k is defined as sum_n x[n+k] * conj(y[n]).
+
         Parameters
         ----------
 
@@ -1737,8 +1738,7 @@ def xcorr(self, x, y, normed=True, detrend=mlab.detrend_none,
             normalization.
 
         normed : boolean, optional, default: True
-            if True, normalize the data by the autocorrelation at the 0-th
-            lag.
+            if True, input vectors are normalised to unit length.
 
         usevlines : boolean, optional, default: True
             if True, Axes.vlines is used to plot the vertical lines from the
