code: def backward(ctx, grad_output):
      gx = _Reduce.apply(ctx.src, ReduceOp.SUM, ctx.group, grad_output)
      if ctx.src != ctx.rank:
          gx.zero_()
      return (None, None, gx)
  
imports: import torch
  import torch.distributed
  from torch.autograd import Function
  from torch.distributed import group, ReduceOp
label_desc: Use image node_id 2 for calling the _Broadcast obj's underlying member method code with example usage: obj.backward(ctx, grad_output) and returns: None,  None,  gx