Walsh character (source code)

= Walsh character
{c}
{title2=$\chi_S$}

For $S\subseteq[n]$, the Walsh character on the <Boolean hypercube> is $\chi_S(x)=\prod_{i\in S}x_i$, equivalently $(-1)^{\sum_{i\in S}x_i}$ in the zero-one convention.