code: def covariance_points(self,x0,y0,xother,yother):
          
  
          cov = np.zeros((len(xother))) + self.nugget
          for v in self.variograms:
              cov += v.covariance_points(x0,y0,xother,yother)
          return cov
docs: Get the covariance between point x0,y0 and the points
          contained in xother, yother.
  
          Parameters
          ----------
          x0 : (float)
              x-coordinate
          y0 : (float)
              y-coordinate
          xother : (iterable of floats)
              x-coordinate of other points
          yother : (iterable of floats)
              y-coordinate of other points
  
          Returns
          -------
          cov : numpy.ndarray
              a 1-D array of covariance between point x0,y0 and the
              points contained in xother, yother.  len(cov) = len(xother) =
              len(yother)