docs: def pysal_Gamma(self, **kwargs):
          """
          Compute Gamma Index of Spatial Autocorrelation for GeoRaster
  
          Usage:
          geo.pysal_Gamma(permutations = 1000, rook=True, operation='c')
  
          arguments passed to raster_weights() and pysal.Gamma
          See help(gr.raster_weights), help(pysal.Gamma) for options
          """
          if self.weights is None:
              self.raster_weights(**kwargs)
          rasterf = self.raster.flatten()
          rasterf = rasterf[rasterf.mask==False]
          self.Gamma = pysal.Gamma(rasterf, self.weights, **kwargs)