code: def forward(self, w, r, attn_mask=None, mems=None):
      raise NotImplementedError
  
imports: import sys
  import math
  import functools
  import numpy
  import torch
  import torch.nn
  import torch.nn.functional
  from proj_adaptive_softmax import ProjectedAdaptiveLogSoftmax, Projection
  from log_uniform_sampler import LogUniformSampler, sample_logits
  from fmoe import FMoETransformerMLP
label_desc: Use image node_id 5 for calling the RelMultiHeadAttn obj's underlying member method code with example usage: obj.forward(w, r, attn_mask, mems) without return types