mindspore.nn.BCEWithLogitsLoss

class mindspore.nn.BCEWithLogitsLoss(reduction='mean', weight=None, pos_weight=None)

Adds sigmoid activation function to input input as logits, and uses the given logits to compute binary cross entropy between the input and the target.

Sets input input as \(X\), input target as \(Y\), output as \(L\). Then,

\[p_{ij} = sigmoid(X_{ij}) = \frac{1}{1 + e^{-X_{ij}}}\]

\[L_{ij} = -[Y_{ij} \cdot \log(p_{ij}) + (1 - Y_{ij}) \cdot \log(1 - p_{ij})]\]

Then,

\[\begin{split}\ell(x, y) = \begin{cases} L, & \text{if reduction} = \text{'none';}\\ \operatorname{mean}(L), & \text{if reduction} = \text{'mean';}\\ \operatorname{sum}(L), & \text{if reduction} = \text{'sum'.} \end{cases}\end{split}\]

Parameters

• reduction (str, optional) –

  Apply specific reduction method to the output: 'none' , 'mean' , 'sum' . Default: 'mean' .

  • 'none': no reduction will be applied.

  • 'mean': compute and return the weighted mean of elements in the output.

  • 'sum': the output elements will be summed.

• weight (Tensor, optional) – A rescaling weight applied to the loss of each batch element. If not None, it can be broadcast to a tensor with shape of input, data type must be float16, float32 or bfloat16(only Atlas A2 series products are supported). Default: None .

• pos_weight (Tensor, optional) – A weight of positive examples. Must be a vector with length equal to the number of classes. If not None, it must be broadcast to a tensor with shape of input, data type must be float16, float32 or bfloat16(only Atlas A2 series products are supported). Default: None .

Inputs:

• input (Tensor) - Input input with shape \((N, *)\) where \(*\) means, any number of additional dimensions. The data type must be float16, float32 or bfloat16(only Atlas A2 series products are supported).

• target (Tensor) - Ground truth label with shape \((N, *)\) where \(*\) means, any number of additional dimensions. The same shape and data type as input.

Outputs:

Tensor or Scalar, if reduction is 'none', its shape is the same as input. Otherwise, a scalar value will be returned.

Raises

• TypeError – If input input or target is not Tensor.

• TypeError – If data type of input or target is not float16, float32 or bfloat16.

• TypeError – If weight or pos_weight is a parameter.

• TypeError – If data type of weight or pos_weight is not float16 , float32 or bfloat16.

• TypeError – If data type of reduction is not string.

• ValueError – If weight or pos_weight can not be broadcast to a tensor with shape of input.

• ValueError – If reduction is not one of 'none', 'mean', 'sum'.

Supported Platforms:

Ascend GPU CPU

Examples

>>> import mindspore as ms
>>> import mindspore.nn as nn
>>> import numpy as np
>>> input = ms.Tensor(np.array([[-0.8, 1.2, 0.7], [-0.1, -0.4, 0.7]]).astype(np.float32))
>>> target = ms.Tensor(np.array([[0.3, 0.8, 1.2], [-0.6, 0.1, 2.2]]).astype(np.float32))
>>> loss = nn.BCEWithLogitsLoss()
>>> output = loss(input, target)
>>> print(output)
0.3463612