# What does this mean?

#### jenniferruurs

What does this sentence mean:

So if ${\cal X}$ is the input space and ${\cal W}$ the set of rules such that for $f\in {\cal W}$ and $x\in {\cal X}$ we have $f(x)\in \{-1,1\}$.

What does $f(x)\in \{-1,1\}$. mean here?

#### skipjack

Forum Staff
I think it means that $f(x)$ is either -1 or 1, but I'd be more confident if I knew the full context.

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