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| Content Provider | ACM Digital Library |
|---|---|
| Author | Williams, Ryan Alman, Josh |
| Abstract | We consider a notion of probabilistic rank and probabilistic sign-rank of a matrix, which measure the extent to which a matrix can be probabilistically represented by low-rank matrices. We demonstrate several connections with matrix rigidity, communication complexity, and circuit lower bounds. The most interesting outcomes are: The Walsh-Hadamard Transform is Not Very Rigid. We give surprising upper bounds on the rigidity of a family of matrices whose rigidity has been extensively studied, and was conjectured to be highly rigid. For the $2^{n}$ à $2^{n}$ Walsh-Hadamard transform $H_{n}$ (a.k.a. Sylvester matrices, a.k.a. the communication matrix of Inner Product modulo 2), we show how to modify only 2ε n entries in each row and make the rank of $H_{n}$ drop below 2n(1â $Ω(ε^{2}/log(1/ε)))},$ for all small ε > 0, over any field. That is, it is not possible to prove arithmetic circuit lower bounds on Hadamard matrices such as $H_{n},$ via L. Valiantâ s matrix rigidity approach. We also show non-trivial rigidity upper bounds for $H_{n}$ with smaller target rank. Matrix Rigidity and Threshold Circuit Lower Bounds. We give new consequences of rigid matrices for Boolean circuit complexity. First, we show that explicit n à n Boolean matrices which maintain rank at least 2(logn)1â δ after $n^{2}/2^{(logn)^{δ/2}}$ modified entries (over any field, for any δ > 0) would yield an explicit function that does not have sub-quadratic-size $AC^{0}$ circuits with two layers of arbitrary linear threshold gates. Second, we prove that explicit 0/1 matrices over the reals which are modestly more rigid than the best known rigidity lower bounds for sign-rank would imply exponential-gate lower bounds for the infamously difficult class of depth-two linear threshold circuits with arbitrary weights on both layers. In particular, we show that matrices defined by these seemingly-difficult circuit classes actually have low probabilistic rank and sign-rank, respectively. An Equivalence Between Communication, Probabilistic Rank, and Rigidity. It has been known since Razborov [1989] that explicit rigidity lower bounds would resolve longstanding lower-bound problems in communication complexity, but it seemed possible that communication lower bounds could be proved without making progress on matrix rigidity. We show that for every function f which is randomly self-reducible in a natural way (the inner product mod 2 is an example), bounding the communication complexity of f (in a precise technical sense) is equivalent to bounding the rigidity of the matrix of f, via an equivalence with probabilistic rank. . |
| Starting Page | 641 |
| Ending Page | 652 |
| Page Count | 12 |
| File Format | |
| ISBN | 9781450345286 |
| DOI | 10.1145/3055399.3055484 |
| Language | English |
| Publisher | Association for Computing Machinery (ACM) |
| Publisher Date | 2017-06-19 |
| Publisher Place | New York |
| Access Restriction | Subscribed |
| Subject Keyword | Threshold circuit Walsh-hadamard transform Matrix rigidity Probabilistic rank |
| Content Type | Text |
| Resource Type | Article |
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