code: def edges_unique(self):
          
          unique, inverse = grouping.unique_rows(self.edges_sorted)
          edges_unique = self.edges_sorted[unique]
          # edges_unique will be added automatically by the decorator
          # additional terms generated need to be added to the cache manually
          self._cache['edges_unique_idx'] = unique
          self._cache['edges_unique_inverse'] = inverse
          return edges_unique
docs: The unique edges of the mesh.
  
          Returns
          ----------
          edges_unique : (n, 2) int
            Vertex indices for unique edges