code: def grid_prep(self):
          
          if len(self.grid_props) == 0:
              return
  
          if self.grid_geostruct is None:
              self.logger.warn("grid_geostruct is None,"\
                    " using ExpVario with contribution=1 and a=(max(delc,delr)*10")
              dist = 10 * float(max(self.m.dis.delr.array.max(),
                                             self.m.dis.delc.array.max()))
              v = pyemu.geostats.ExpVario(contribution=1.0,a=dist)
              self.grid_geostruct = pyemu.geostats.GeoStruct(variograms=v)
docs: prepare grid-based parameterizations