mindspore.ops.BinaryCrossEntropy

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class mindspore.ops.BinaryCrossEntropy(reduction='mean')[source]

Computes the binary cross entropy between the logits and the labels.

Sets logits as \(x\), labels as \(y\), output as \(\ell(x, y)\). Let,

\[L = \{l_1,\dots,l_N\}^\top, \quad l_n = - w_n \left[ y_n \cdot \log x_n + (1 - y_n) \cdot \log (1 - x_n) \right]\]

In which, \(L\) indicates the loss of all batch_sizes, \(l\) indicates the loss of one batch_size, and n indicates one batch_size in the 1-N range, \(w_n\) indicates the weight of \(n\)-th batch of binary cross entropy. Then,

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

Warning

  • The value of \(x\) must range from 0 to 1.

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.

Inputs:

  • logits (Tensor) - The predictive value whose data type must be float16 or float32, The shape is \((N, *)\) where \(*\) means, any number of additional dimensions.

  • labels (Tensor) - The target value which has the same shape and data type as logits.

  • weight (Tensor, optional) - A rescaling weight applied to the loss of each batch element. And it must have the same shape and data type as logits. Default: None .

Outputs:

Tensor or Scalar. Returns Tensor that has the same dtype and shape as logits if reduction is ‘none’. Otherwise, returns a scalar Tensor.

Raises

  • TypeError – If dtype of logits, labels or weight (if given) is neither float16 nor float32.

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

  • ValueError – If shape of labels is not the same as logits or weight (if given).

  • TypeError – If logits, labels or weight is not a Tensor.

Supported Platforms:

Ascend GPU CPU

Examples

>>> import mindspore
>>> import numpy as np
>>> from mindspore import Tensor, nn, ops
>>> class Net(nn.Cell):
...     def __init__(self):
...         super(Net, self).__init__()
...         self.binary_cross_entropy = ops.BinaryCrossEntropy()
...     def construct(self, logits, labels, weight):
...         result = self.binary_cross_entropy(logits, labels, weight)
...         return result
...
>>> net = Net()
>>> logits = Tensor(np.array([0.2, 0.7, 0.1]), mindspore.float32)
>>> labels = Tensor(np.array([0., 1., 0.]), mindspore.float32)
>>> weight = Tensor(np.array([1, 2, 2]), mindspore.float32)
>>> output = net(logits, labels, weight)
>>> print(output)
0.38240486