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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def dtime(sdat, tstart=None, tend=None):
 """Time increment dt. Compute dt as a function of time. 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`: dt and time arrays. """

    tseries = sdat.tseries_between(tstart, tend)
    time = tseries['t'].values
    return time[1:] - time[:-1], time[:-1]