Set limits for the x-axis.

        :param min: minimum value to be displayed.  If None, it will be
            calculated.
        :param max: maximum value to be displayed.  If None, it will be
            calculated.

def set_xlimits(self, min=None, max=None):
        """Set limits for the x-axis.

        :param min: minimum value to be displayed.  If None, it will be
            calculated.
        :param max: maximum value to be displayed.  If None, it will be
            calculated.

        """
        self.limits['xmin'] = min
        self.limits['xmax'] = max