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I'm reading the paper A Neural Attention Model for Sentence Summarization (Rush et al., EMNLP 2015) and came across the following:

Let the input consist of a sequence of $M$ words $\mathbf{x}_1, \dots , \mathbf{x}_M$ coming form a fixed vocabulary $\mathcal{V}$ of size $\vert \mathcal{V} \vert = V$. We will represent each word as an indicator vector $\mathbf{x}_i \in \{0, 1\}^V$ for $i \in \{1, \dots, M\}$, sentences as a sequence of indicators, and $\mathcal{X}$ as the set of possible inputs.

What does it mean to represent words as "indicator vectors?" The Wikipedia page for indicator vectors says that an indicator vector is basically a vector for a subset $T$ of set $S$ that is $0$ or $1$ depending on whether that element in $T$ is also in $S$.

Does the paper mean that each word is a one hot vector for the vocabulary? Thanks.

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Exactly, each word is represented by a one hot vector of size $V$. In your quote, $\mathbf x_i\in \{0,1\}^V$ signifies this.

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  • $\begingroup$ That's also what I thought because nothing else makes sense. However, doesn't that notation mean that $\mathbf{x}_i$ is a binary vector rather than a one-hot vector? The notation is just what confused me. $\endgroup$
    – Sean
    Commented Jun 5, 2020 at 2:20

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