docs: def dt_dt(sdat, tstart=None, tend=None):
      """Derivative of temperature.
  
      Compute dT/dt as a function of time using an explicit Euler scheme.
  
      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`: derivative of temperature and time
          arrays.
      """
      tseries = sdat.tseries_between(tstart, tend)
      time = tseries['t'].values
      temp = tseries['Tmean'].values
      dtdt = (temp[1:] - temp[:-1]) / (time[1:] - time[:-1])
      return dtdt, time[:-1]