code: def focal_loss(
      cls_output: torch.Tensor,
      cls_targets_at_level: torch.Tensor,
      num_positive_sum: torch.Tensor,
      num_real_classes: int,
      alpha: float,
      gamma: float,
      label_smoothing: float = 0.0,
  ) -> torch.Tensor:
      """Fused focal loss function."""
      return FocalLoss.apply(
          cls_output,
          cls_targets_at_level,
          num_positive_sum,
          num_real_classes,
          alpha,
          gamma,
          label_smoothing,
      )
  
imports: import torch
  import focal_loss_cuda
label_desc: Use image node_id 1 for calling a global function with example usage: focal_loss(cls_output, cls_targets_at_level, num_positive_sum, num_real_classes, alpha, gamma, label_smoothing) and returns: FocalLoss