class paddle.nn. SmoothL1Loss ( reduction='mean', delta=1.0, name=None ) [source]

This operator calculates smooth_l1_loss. Creates a criterion that uses a squared term if the absolute element-wise error falls below 1 and an L1 term otherwise. In some cases it can prevent exploding gradients and it is more robust and less sensitivity to outliers. Also known as the Huber loss:

\[\begin{split}loss(x,y) = \\frac{1}{n}\\sum_{i}z_i\end{split}\]

where z_i is given by:

\[\begin{split} \\mathop{z_i} = \\left\\{\\begin{array}{rcl} 0.5(x_i - y_i)^2 & & {if |x_i - y_i| < delta} \\\\ delta * |x_i - y_i| - 0.5 * delta^2 & & {otherwise} \\end{array} \\right.\end{split}\]
  • reduction (str, optional) – Indicate how to average the loss by batch_size, the candicates are 'none' | 'mean' | 'sum'. If reduction is 'mean', the reduced mean loss is returned; If reduction is 'sum', the reduced sum loss is returned. If reduction is 'none', the unreduced loss is returned. Default is 'mean'.

  • delta (float, optional) – Specifies the hyperparameter delta to be used. The value determines how large the errors need to be to use L1. Errors smaller than delta are minimized with L2. Parameter is ignored for negative/zero values. Default = 1.0

  • name (str, optional) – Name for the operation (optional, default is None). For more information, please refer to Name.

Call Parameters:
input (Tensor): Input tensor, the data type is float32 or float64. Shape is

(N, C), where C is number of classes, and if shape is more than 2D, this is (N, C, D1, D2,…, Dk), k >= 1.

label (Tensor): Label tensor, the data type is float32 or float64. The shape of label

is the same as the shape of input.


The tensor storing the smooth_l1_loss of input and label.

Return type: Tensor.


import paddle
import numpy as np
input_data = np.random.rand(3,3).astype("float32")
label_data = np.random.rand(3,3).astype("float32")
input = paddle.to_tensor(input_data)
label = paddle.to_tensor(label_data)
loss = paddle.nn.SmoothL1Loss()
output = loss(input, label)
forward ( input, label )

Defines the computation performed at every call. Should be overridden by all subclasses.

  • *inputs (tuple) – unpacked tuple arguments

  • **kwargs (dict) – unpacked dict arguments