docstr: Forward function to calculate accuracy.
  
  Args:
      pred (torch.Tensor): Prediction of models.
      target (torch.Tensor): Target for each prediction.
  
  Returns:
      tuple[float]: The accuracies under different topk criterions.
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code: def forward(self, pred, target):
      """Forward function to calculate accuracy.
  
      Args:
          pred (torch.Tensor): Prediction of models.
          target (torch.Tensor): Target for each prediction.
  
      Returns:
          tuple[float]: The accuracies under different topk criterions.
      """
      return accuracy(pred, target, self.topk, self.thresh)
  
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  from ppdet.modeling.initializer import constant_
  from paddle.nn.initializer import KaimingNormal
  import paddle.nn
label_desc: Use image node_id 2 for calling the Accuracy obj's underlying member method code with example usage: obj.forward(pred, target) and returns: accuracy