def twiny(self):
ax2 = self.figure.add_axes(self.get_position(True), sharey=self,<EOL>frameon=False)<EOL>ax2.xaxis.tick_top()<EOL>ax2.xaxis.set_label_position('<STR_LIT>')<EOL>self.xaxis.tick_bottom()<EOL>return ax2<EOL>
call signature::

  ax = twiny()

create a twin of Axes for generating a plot with a shared
y-axis but independent x axis.  The x-axis of self will have
ticks on bottom and the returned axes will have ticks on the
top