code: def to_array(self):
          
          values = numpy.empty(13, dtype=float)
          values[:6] = self.firstdate.to_array()
          values[6:12] = self.lastdate.to_array()
          values[12] = self.stepsize.seconds
          return values
docs: Returns a 1-dimensional |numpy| |numpy.ndarray| with thirteen
          entries first defining the start date, secondly defining the end
          date and thirdly the step size in seconds.