def mobility(sdat, tstart=None, tend=None):
tseries = sdat.tseries_between(tstart, tend)<EOL>steps = sdat.steps[tseries.index[<NUM_LIT:0>]:tseries.index[-<NUM_LIT:1>]]<EOL>time = []<EOL>mob = []<EOL>for step in steps.filter(rprof=True):<EOL><INDENT>time.append(step.timeinfo['<STR_LIT:t>'])<EOL>mob.append(step.rprof.iloc[-<NUM_LIT:1>].loc['<STR_LIT>'] / step.timeinfo['<STR_LIT>'])<EOL><DEDENT>return np.array(mob), np.array(time)<EOL>
Plates mobility.

    Compute the ratio vsurf / vrms.

    Args:
        sdat (:class:`~stagpy.stagyydata.StagyyData`): a StagyyData instance.
        tstart (float): time at which the computation should start. Use the
            beginning of the time series data if set to None.
        tend (float): time at which the computation should end. Use the
            end of the time series data if set to None.
    Returns:
        tuple of :class:`numpy.array`: mobility and time arrays.