chainer.functions.black_out¶

chainer.functions.black_out(x, t, W, samples, reduce='mean')[source]

BlackOut loss function.

BlackOut loss function is defined as

$-\log(p(t)) - \sum_{s \in S} \log(1 - p(s)),$

where $$t$$ is the correct label, $$S$$ is a set of negative examples and $$p(\cdot)$$ is likelihood of a given label. And, $$p$$ is defined as

$p(y) = \frac{\exp(W_y^\top x)}{ \sum_{s \in samples} \exp(W_s^\top x)}.$

The output is a variable whose value depends on the value of the option reduce. If it is 'no', it holds the no loss values. If it is 'mean', this function takes a mean of loss values.

Parameters
• x (Variable or N-dimensional array) – Batch of input vectors. Its shape should be $$(N, D)$$.

• t (Variable or N-dimensional array) – Vector of ground truth labels. Its shape should be $$(N,)$$. Each elements $$v$$ should satisfy $$0 \geq v \geq V$$ or $$-1$$ where $$V$$ is the number of label types.

• W (Variable or N-dimensional array) – Weight matrix. Its shape should be $$(V, D)$$

• samples (Variable) – Negative samples. Its shape should be $$(N, S)$$ where $$S$$ is the number of negative samples.

• reduce (str) – Reduction option. Its value must be either 'no' or 'mean'. Otherwise, ValueError is raised.

Returns

A variable object holding loss value(s). If reduce is 'no', the output variable holds an array whose shape is $$(N,)$$ . If it is 'mean', it holds a scalar.

Return type

Variable