code: def backward(ctx, grad_output):
      (posterior,) = ctx.saved_tensors
      grad_logp = grad_output.unsqueeze(ctx.dim) * posterior
      return grad_logp, None, None
  
imports: import torch
label_desc: Use image node_id 2 for calling the LogSumExpMoE obj's underlying member method code with example usage: obj.backward(ctx, grad_output) and returns: grad_logp,  None,  None