def plot_grid(step):
    """Plot cell position and thickness.

    The figure is call grid_N.pdf where N is replace by the step index.

    Args:
        step (:class:`~stagpy.stagyydata._Step`): a step of a StagyyData
            instance.
    """
    rad = get_rprof(step, 'r')[0]
    drad = get_rprof(step, 'dr')[0]
    _, unit = step.sdat.scale(1, 'm')
    if unit:
        unit = ' ({})'.format(unit)
    fig, (ax1, ax2) = plt.subplots(2, sharex=True)
    ax1.plot(rad, '-ko')
    ax1.set_ylabel('$r$' + unit)
    ax2.plot(drad, '-ko')
    ax2.set_ylabel('$dr$' + unit)
    ax2.set_xlim([-0.5, len(rad) - 0.5])
    ax2.set_xlabel('Cell number')
    misc.saveplot(fig, 'grid', step.istep)
Plot cell position and thickness.

    The figure is call grid_N.pdf where N is replace by the step index.

    Args:
        step (:class:`~stagpy.stagyydata._Step`): a step of a StagyyData
            instance.