I just discovered that a legend with label '$-$', i.e., a single math-mode minus sign, has a number of problems in png output (which also is problematic for ipython ...
Qt Version : 4.8.6, PyQt4 (API v2) 4.10.4 on Darwin File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/pyplot.py ...
一部の結果でアクセス不可の可能性があるため、非表示になっています。
アクセス不可の結果を表示する