提交 c67c54a8 编写于 作者: Y Yibing Liu

Polish the doc of cross_entropy

上级 95862a54
......@@ -270,6 +270,7 @@ def gru_unit(input,
attr=helper.param_attr, shape=[size, 3 * size], dtype=dtype)
# create bias
if bias is None:
bias_size = [1, 3 * size]
bias = helper.create_parameter(
......@@ -358,7 +359,59 @@ def cos_sim(X, Y, **kwargs):
def cross_entropy(input, label, **kwargs):
"""
This function computes cross_entropy using the input and label.
**Cross Entropy Layer**
This layer computes the cross entropy between `input` and `label`. It supports
both standard cross-entropy and soft-label cross-entropy loss computation.
1) One-hot cross-entropy:
`soft_label = false`, `Label[i, 0]` indicates the class index for sample i:
.. math::
Y[i] = -\log(X[i, Label[i]])
2) Soft-label cross-entropy:
`soft_label = true`, `Label[i, j]` indicates the soft label of class j
for sample i:
.. math::
Y[i] = \sum_j{-Label[i, j] * log(X[i, j])}
Please make sure that in this case the summuation of each row of `label`
equals one.
3) One-hot cross-entropy with vecterized `label`:
As a special case of 2), when each row of 'label' has only one
non-zero element (equals 1), soft-label cross-entropy degenerates to a
one-hot cross-entropy with one-hot label representation.
Args:
input (Variable|list): a 2-D tensor with shape N x D, where N is the
batch size and D is the number of classes. This input is a probability
computed by the previous operator, which is almost always the result
of a softmax operator.
label (Variable|list): the ground truth which is a 2-D tensor. When
`soft_label` is set to `false`, `label` is a tensor<int64> with shape
[N x 1]. When `soft_label` is set to `true`, `label` is a
tensor<float/double> with shape [N x K].
soft_label (bool, via `**kwargs`): a flag indicating whether to interpretate
the given labels as soft labels, default `false`.
Returns:
A 2-D tensor with shape [N x 1], the cross entropy loss.
Raises:
`ValueError`: 1) If the 1st dimension of `input` and `label` are not equal; 2) If
`soft_label == true`, and the 2nd dimension of `input` and `label` are not
equal; 3) If `soft_label == false`, and the 2nd dimension of `label` is not 1.
Examples:
.. code-block:: python
predict = fluid.layers.fc(input=net, size=classdim, act='softmax')
cost = fluid.layers.cross_entropy(input=predict, label=label)
"""
helper = LayerHelper('cross_entropy', **kwargs)
out = helper.create_tmp_variable(dtype=input.dtype)
......
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