class_docstr: Lunar Multi-headed attention.
  See "Linformer: Self-Attention with Linear Complexity" for more details.
code: def prepare_for_onnx_export_(self):
      self.onnx_trace = True
      raise NotImplementedError(
          "onnx for linear attention not implemented"
      )
  
imports: import math
  from typing import Dict, Optional, Tuple, Union
  import torch
  import torch.nn.functional
  from fairseq import utils
  from fairseq.incremental_decoding_utils import with_incremental_state
  from fairseq.modules.fairseq_dropout import FairseqDropout
  from torch import nn, Tensor
label_desc: Use image node_id 2 for calling the LunarMultiheadAttention obj's underlying member method code with example usage: obj.prepare_for_onnx_export_() without return types