code: def _h_function(self,h):
          
          return self.contribution * np.exp(-1.0 * h / self.a)
docs: private method exponential variogram "h" function
  
          Parameters
          ----------
          h : (float or numpy.ndarray)
              distance(s)
  
          Returns
          -------
          h_function : float or numpy.ndarray
              the value of the "h" function implied by the ExpVario