code: def cbow_batch(centers, contexts, num_tokens, dtype, index_dtype):
      
      contexts_data, contexts_row, contexts_col = contexts
      centers = mx.nd.array(centers, dtype=index_dtype)
      contexts = mx.nd.sparse.csr_matrix(
          (contexts_data, (contexts_row, contexts_col)),
          dtype=dtype, shape=(len(centers), num_tokens))  # yapf: disable
      return centers, contexts
docs: Create a batch for CBOW training objective.