# News for April 2016

April has been kind to us, providing us with a trio of new papers in sublinear algorithms. Also, in case you missed them, be sure to check out Oded Goldreich’s guest post and the associated open problem.

Sparse Fourier Transform in Any Constant Dimension with Nearly-Optimal Sample Complexity in Sublinear Time, by Michael Kapralov (ArXiv). There is a rich line of work focused on going beyond the celebrated Fast Fourier Transform algorithm by exploiting sparsity in the signal’s Fourier representation. While the one-dimensional case is very well understood, results in higher dimensions have either been lacking with respect to time complexity, sample complexity, or the approximation guarantee. This work is the first to give an algorithm which runs in sublinear time, has near-optimal sample complexity, and provides an arbitrarily accurate approximation guarantee for the multivariate case.

Sublinear Time Estimation of Degree Distribution Moments: The Arboricity Connection, by Talya Eden, Dana Ron, C. Seshadhri (ArXiv). This work revisits the problem of approximating the moments of the degree distribution of a graph. Prior work has shown that the $$s$$-th moment of the degree distribution can be computed with $$\tilde O(n^{1 – 1/(s+1)})$$ queries, which is optimal up to $$\mathrm{poly}(\log n)$$ factors. This work provides a new algorithm which requires only $$\tilde O(n^{1 – 1/s})$$ queries on graphs of bounded arboricity, while still matching previous near-optimal bounds in the worst case. Impressively, the algorithm is incredibly simple, and can be stated in just a few lines of pseudocode.

A Local Algorithm for Constructing Spanners in Minor-Free Graphs, by Reut Levi, Dana Ron, Ronitt Rubinfeld (ArXiv). This paper addresses the problem of locally constructing a sparse spanning graph. For an edge $$e$$ in a graph $$G$$, one must determine whether or not $$e$$ is in a sparse spanning graph $$G’$$ in a manner that is consistent with previous answers. In general graphs, the complexity of this problem is $$\Omega(\sqrt{n})$$, leading to the study of restricted families of graphs. In minor-free graphs (which include, for example, planar graphs), existing algorithms require $$(d/\varepsilon)^{\mathrm{poly}(h)\log(1/\varepsilon)}$$ queries and induce a stretch of $$\mathrm{poly}(d, h, 1/\varepsilon)$$, where $$d$$ is the maximum degree, $$h$$ is the size of the minor, and $$G’$$ is of size at most $$(1 + \varepsilon)n$$. The algorithm in this paper shows the complexity of this problem to be polynomial, requiring only $$\mathrm{poly}(d, h, 1/\varepsilon)$$ queries and inducing a stretch of $$\tilde O(h \log (d)/\varepsilon)$$.