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FocalLoss

class mmcls.models.FocalLoss(gamma=2.0, alpha=0.25, reduction='mean', loss_weight=1.0)[source]

Focal loss.

Parameters
  • gamma (float) – Focusing parameter in focal loss. Defaults to 2.0.

  • alpha (float) – The parameter in balanced form of focal loss. Defaults to 0.25.

  • reduction (str) – The method used to reduce the loss into a scalar. Options are “none” and “mean”. Defaults to ‘mean’.

  • loss_weight (float) – Weight of loss. Defaults to 1.0.

forward(pred, target, weight=None, avg_factor=None, reduction_override=None)[source]

Sigmoid focal loss.

Parameters
  • pred (torch.Tensor) – The prediction with shape (N, *).

  • target (torch.Tensor) – The ground truth label of the prediction with shape (N, *), N or (N,1).

  • weight (torch.Tensor, optional) – Sample-wise loss weight with shape (N, *). Defaults to None.

  • avg_factor (int, optional) – Average factor that is used to average the loss. Defaults to None.

  • reduction_override (str, optional) – The method used to reduce the loss into a scalar. Options are “none”, “mean” and “sum”. Defaults to None.

Returns

Loss.

Return type

torch.Tensor

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