def advth(step):
rbot, rtop = misc.get_rbounds(step)<EOL>rmean = <NUM_LIT:0.5> * (rbot + rtop)<EOL>rad = step.rprof['<STR_LIT:r>'].values + rbot<EOL>radio = step.timeinfo['<STR_LIT>']<EOL>if rbot != <NUM_LIT:0>:  <EOL><INDENT>th_adv = -(rtop**<NUM_LIT:3> - rad**<NUM_LIT:3>) / rmean**<NUM_LIT:2> / <NUM_LIT:3><EOL><DEDENT>else:<EOL><INDENT>th_adv = rad - rtop<EOL><DEDENT>th_adv *= radio<EOL>th_adv += step.timeinfo['<STR_LIT>']<EOL>return th_adv, None<EOL>
Theoretical advection.

    This compute the theoretical profile of total advection as function of
    radius.

    Args:
        step (:class:`~stagpy.stagyydata._Step`): a step of a StagyyData
            instance.
    Returns:
        tuple of :class:`numpy.array` and None: the theoretical advection.
        The second element of the tuple is None.