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Paper:

TR25-036 | 29th March 2025 06:33

Lifting for Arbitrary Gadgets

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TR25-036
Authors: Siddharth Iyer
Publication: 29th March 2025 21:14
Downloads: 148
Keywords: 


Abstract:

We prove a sensitivity-to-communication lifting theorem for arbitrary gadgets. Given functions $f: \{0,1\}^n\to \{0,1\}$ and $g : \mathcal{X} \times \mathcal{Y}\to \{0,1\}$, denote $f\circ g(x,y) := f(g(x_1,y_1),\ldots,g(x_n,y_n))$. We show that for any $f$ with sensitivity $s$ and any $g$,
\[D(f\circ g) \geq s\cdot \bigg(\frac{\Omega(D(g))}{\log rk(g)} - \log rk(g)\bigg),\]
where $D(\cdot)$ denotes the deterministic communication complexity and $rk(g)$ is the rank of the matrix associated with $g$.
As a corollary, we get that if $D(g)$ is a sufficiently large constant, $D(f\circ g) = \Omega(\min\{s,d\}\cdot \sqrt{D(g)})$, where $s$ and $d$ denote the sensitivity and degree of $f$. In particular, computing the OR of $n$ copies of $g$ requires $\Omega(n\cdot\sqrt{D(g)})$ bits.



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