Neural networks


Self-attention is a weighted average of all input elements from a sequence, with a weight proportional to a similarity score between representations. The input \(x \in \mathbb{R}^{L \times F}\) is projected by matrices \(W_Q \in \mathbb{R}^{F \times D}\), \(W_K \in \mathbb{R}^{F\times D}\) and \(W_V \in \mathbb{R}^{F\times M}\) to representations \(Q\) (queries), \(K\) (keys) and \(V\) (values).

\[ Q = xW_Q\] \[ K = xW_K\] \[ V = xW_V\]

Output for all positions in a sequence \(x\), is written

\[A(x) = V' = \text{softmax}\left( \dfrac{QK^{T}}{\sqrt{D}} \right) V.\]

The softmax is applied row-wise in the equation above.

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