def r_edges(step):
rbot, rtop = misc.get_rbounds(step)<EOL>centers = step.rprof.loc[:, '<STR_LIT:r>'].values + rbot<EOL>edges = (centers[:-<NUM_LIT:1>] + centers[<NUM_LIT:1>:]) / <NUM_LIT:2><EOL>edges = np.insert(edges, <NUM_LIT:0>, rbot)<EOL>edges = np.append(edges, rtop)<EOL>return edges, edges<EOL>
Cell border.

    Args:
        step (:class:`~stagpy.stagyydata._Step`): a step of a StagyyData
            instance.
    Returns:
        tuple of :class:`numpy.array`: the position of the bottom and top walls
        of the cells. The two elements of the tuple are identical.