TST: fix tests, make them modern

jklymak · jklymak · commit be9c155d62bc · 2018-03-24T21:09:28.000-07:00
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -1673,7 +1673,8 @@ 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
-        
+        :math:`\sum_n x[n+k] \cdot y^*[n]`, where :math:`y^*` is the complex
+        conjugate of :math:`y`.
 
         Parameters
         ----------
