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| Content Provider | ACM Digital Library |
|---|---|
| Author | Indyk, Piotr Cheraghchi, Mahdi |
| Abstract | For every fixed constant α > 0, we design an algorithm for computing the k-sparse Walsh-Hadamard transform (i.e., Discrete Fourier Transform over the Boolean cube) of an N-dimensional vector x ∈ $R^{N}$ in time $k^{1+α}(log$ $N)^{O(1)}.$ Specifically, the algorithm is given query access to x and computes a k-sparse x ∈ $R^{N}$ satisfying $||[EQUATION]||_{1}$ ≤c||[EQUATION] -- $H_{k}([EQUATION])||_{1},$ for an absolute constant c > 0, where [EQUATION] is the transform of x and $H_{k}([EQUATION])$ is its best k-sparse approximation. Our algorithm is fully deterministic and only uses non-adaptive queries to x (i.e., all queries are determined and performed in parallel when the algorithm starts). An important technical tool that we use is a construction of nearly optimal and linear lossless condensers which is a careful instantiation of the GUV condenser (Guruswami, Umans, Vadhan, JACM 2009). Moreover, we design a deterministic and non-adaptive $ℓ_{1}/ℓ_{1}$ compressed sensing scheme based on general lossless condensers that is equipped with a fast reconstruction algorithm running in time $k^{1+α}(log$ $N)^{O(1)}$ (for the GUV-based condenser) and is of independent interest. Our scheme significantly simplifies and improves an earlier expander-based construction due to Berinde, Gilbert, Indyk, Karloff, Strauss (Allerton 2008). Our methods use linear lossless condensers in a black box fashion; therefore, any future improvement on explicit constructions of such condensers would immediately translate to improved parameters in our framework (potentially leading to k(log $N)^{O(1)}$ reconstruction time with a reduced exponent in the poly-logarithmic factor, and eliminating the extra parameter α). By allowing the algorithm to use randomness, while still using non-adaptive queries, the running time of the algorithm can be improved to Õ(k $log^{3}$ N). |
| Ending Page | 317 |
| Page Count | 20 |
| Starting Page | 298 |
| File Format | |
| ISBN | 9781611974331 |
| Language | English |
| Publisher | Association for Computing Machinery (ACM) |
| Publisher Date | 2016-01-10 |
| Access Restriction | Subscribed |
| Content Type | Text |
| Resource Type | Article |
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