def clear_matplotlib_ticks(ax=None, axis='both'):
    """
    Clears the default matplotlib axes, or the one specified by the axis
    argument.

    Parameters
    ----------
    ax: Matplotlib AxesSubplot, None
        The subplot to draw on.
    axis: string, "both"
        The axis to clear: "x" or "horizontal", "y" or "vertical", or "both"
    """
    if not ax:
        return
    if axis.lower() in ['both', 'x', 'horizontal']:
        ax.set_xticks([], [])
    if axis.lower() in ['both', 'y', 'vertical']:
        ax.set_yticks([], [])
