Backport PR #12775: Add note to errorbar function about sign of errors (#12783)

meeseeksmachine · timhoffm · commit beb254a8baf2 · 2018-11-09T20:50:11.000+01:00
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -2949,6 +2949,8 @@ def errorbar(self, x, y, yerr=None, xerr=None,
                 upper errors.
             - *None*: No errorbar.
 
+            Note that all error arrays should have *positive* values.
+
             See :doc:`/gallery/statistics/errorbar_features`
             for an example on the usage of ``xerr`` and ``yerr``.
 
