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 matrix-vector product


Faster Linear Algebra for Distance Matrices

Neural Information Processing Systems

The distance matrix of a dataset $X$ of $n$ points with respect to a distance function $f$ represents all pairwise distances between points in $X$ induced by $f$. Due to their wide applicability, distance matrices and related families of matrices have been the focus of many recent algorithmic works. We continue this line of research and take a broad view of algorithm design for distance matrices with the goal of designing fast algorithms, which are specifically tailored for distance matrices, for fundamental linear algebraic primitives. Our results include efficient algorithms for computing matrix-vector products for a wide class of distance matrices, such as the $\ell_1$ metric for which we get a linear runtime, as well as an $\Omega(n^2)$ lower bound for any algorithm which computes a matrix-vector product for the $\ell_{\infty}$ case, showing a separation between the $\ell_1$ and the $\ell_{\infty}$ metrics. Our upper bound results in conjunction with recent works on the matrix-vector query model have many further downstream applications, including the fastest algorithm for computing a relative error low-rank approximation for the distance matrix induced by $\ell_1$ and $\ell_2^2$ functions and the fastest algorithm for computing an additive error low-rank approximation for the $\ell_2$ metric, in addition to applications for fast matrix multiplication among others. We also give algorithms for constructing distance matrices and show that one can construct an approximate $\ell_2$ distance matrix in time faster than the bound implied by the Johnson-Lindenstrauss lemma.







A Algorithms

Neural Information Processing Systems

Below we include detailed pseudocode for algorithms described in the main text.Algorithm 2 Parameter Free DeltaShift Input: Implicit matrix-vector multiplication access to A In this section, we give a full proof of Theorem 1.1 with the correct logarithmic dependence on Before doing so, we collect several definitions and results required for proving the theorem. As discussed, a tight analysis of Hutchinson's estimator, and also our DeltaShift algorithm, relies Finally, from Claim B.2, we immediately have Rademacher random vectors, a similar analysis can be performed for any i.i.d. Now, we are ready to move on to the main result. The proof is by induction. We claim that, for all j = 1,...,m, t Next consider the inductive case.