code: def covariance(self,pt0,pt1):
          
  
          x = np.array([pt0[0],pt1[0]])
          y = np.array([pt0[1],pt1[1]])
          names = ["n1","n2"]
          return self.covariance_matrix(x,y,names=names).x[0,1]
docs: get the covarince between two points implied by Vario2d
  
          Parameters
          ----------
          pt0 : (iterable of len 2)
              first point x and y
          pt1 : (iterable of len 2)
              second point x and y
  
          Returns
          -------
          cov : float
              covariance between pt0 and pt1