get a cheap plot of the Vario2d

        Parameters
        ----------
        **kwargs : (dict)
            keyword arguments to use for plotting

        Returns
        -------
        ax : matplotlib.pyplot.axis

        Note
        ----
        optional arguments in kwargs include
        "ax" (existing matplotlib.pyplot.axis).  Other
        kwargs are passed to matplotlib.pyplot.plot()

def plot(self,**kwargs):
        """ get a cheap plot of the Vario2d

        Parameters
        ----------
        **kwargs : (dict)
            keyword arguments to use for plotting

        Returns
        -------
        ax : matplotlib.pyplot.axis

        Note
        ----
        optional arguments in kwargs include
        "ax" (existing matplotlib.pyplot.axis).  Other
        kwargs are passed to matplotlib.pyplot.plot()

        """
        try:
            import matplotlib.pyplot as plt
        except Exception as e:
            raise Exception("error importing matplotlib: {0}".format(str(e)))

        ax = kwargs.pop("ax",plt.subplot(111))
        x = np.linspace(0,self.a*3,100)
        y = self.inv_h(x)
        ax.set_xlabel("distance")
        ax.set_ylabel("$\gamma$")
        ax.plot(x,y,**kwargs)
        return ax