code: def _initialize_splittable_dimensions(self, mtf_graph):
      
      all_mtf_dimension_names = set()  # set(string)
      for mtf_operation in mtf_graph.operations:
        for mtf_tensor in mtf_operation.outputs:
          for mtf_dimension in mtf_tensor.shape.dims:
            if not re.match(r"_anonymous_\d*", mtf_dimension.name):
              all_mtf_dimension_names.add(mtf_dimension.name)
  
      unsplittable_mtf_dimension_names = set()  # set(string)
      for mtf_operation in mtf_graph.operations:
        unsplittable_mtf_dimension_names.update(mtf_operation.unsplittable_dims)
  
      return all_mtf_dimension_names - unsplittable_mtf_dimension_names
docs: Initializer for self._splittable_mtf_dimension_names.
  
      Args:
        mtf_graph: an mtf.Graph.
  
      Returns:
        A set(string) of the names of Mesh TensorFlow dimensions that may be
        assigned in a layout.