class_docstr: The abstract sparse optimizer.
  
  Note: dgl sparse optimizer only work with dgl.NodeEmbedding
  
  Parameters
  ----------
  params : list of NodeEmbedding
      The list of NodeEmbeddings.
  lr : float
      The learning rate.
code: def _comm_setup(self):
      self._comm = True
  
imports: import abc
  from abc import abstractmethod
  import torch
  from ...cuda import nccl
  from ...nn.pytorch import NodeEmbedding
  from ...partition import NDArrayPartition
  from ...utils import create_shared_mem_array, gather_pinned_tensor_rows, get_shared_mem_array, pin_memory_inplace, scatter_pinned_tensor_rows
label_desc: Use image node_id 4 for calling the SparseGradOptimizer obj's underlying member method code with example usage: obj._comm_setup() without return types