paper-BagRelationalPDBsAreHard/app_onepass_eval-notes.tex

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The evaluation of $\abs{\circuit}(1,\ldots, 1)$ can be defined recursively, as follows (where $\circuit_\linput$ and $\circuit_\rinput$ are the `left' and `right' inputs of $\circuit$ if they exist):
{\small
\begin{align}
\label{eq:T-all-ones}
\abs{\circuit}(1,\ldots, 1) = \begin{cases}
\abs{\circuit_\linput}(1,\ldots, 1) \cdot \abs{\circuit_\rinput}(1,\ldots, 1) &\textbf{if }\circuit.\type = \circmult\\
\abs{\circuit_\linput}(1,\ldots, 1) + \abs{\circuit_\rinput}(1,\ldots, 1) &\textbf{if }\circuit.\type = \circplus \\
|\circuit.\val| &\textbf{if }\circuit.\type = \tnum\\
1 &\textbf{if }\circuit.\type = \var.
\end{cases}
\end{align}
}
It turns out that for proof of \Cref{lem:sample}, we need to argue that when $\circuit.\type = +$, we indeed have
\begin{align}
\label{eq:T-weights}
\circuit.\lwght &\gets \frac{\abs{\circuit_\linput}(1,\ldots, 1)}{\abs{\circuit_\linput}(1,\ldots, 1) + \abs{\circuit_\rinput}(1,\ldots, 1)};\\
\circuit.\rwght &\gets \frac{\abs{\circuit_\rinput}(1,\ldots, 1)}{\abs{\circuit_\linput}(1,\ldots, 1)+ \abs{\circuit_\rinput}(1,\ldots, 1)}
\end{align}