Abstract
Parallel fixedparameter tractability studies how parameterized problems can be solved in parallel. A surprisingly large number of parameterized problems admit a high level of parallelization, but this does not mean that we can also efficiently compute small problem kernels in parallel: known kernelization algorithms are typically highly sequential. In the present paper, we establish a number of upper and lower bounds concerning the sizes of kernels that can be computed in parallel. An intriguing finding is that there are complex tradeoffs between kernel size and the depth of the circuits needed to compute them: For the vertex cover problem, an exponential kernel can be computed by AC^0circuits, a quadratic kernel by TC^0circuits, and a linear kernel by randomized NCcircuits with derandomization being possible only if it is also possible for the matching problem. Other natural problems for which similar (but quantitatively different) effects can be observed include tree decomposition problems parameterized by the vertex cover number, the undirected feedback vertex set problem, the matching problem, or the point line cover problem. We also present natural problems for which computing kernels is inherently sequential.
BibTeX  Entry
@InProceedings{bannach_et_al:LIPIcs:2019:10214,
author = {Max Bannach and Till Tantau},
title = {{Computing Kernels in Parallel: Lower and Upper Bounds}},
booktitle = {13th International Symposium on Parameterized and Exact Computation (IPEC 2018)},
pages = {13:113:14},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {9783959770842},
ISSN = {18688969},
year = {2019},
volume = {115},
editor = {Christophe Paul and Michal Pilipczuk},
publisher = {Schloss DagstuhlLeibnizZentrum fuer Informatik},
address = {Dagstuhl, Germany},
URL = {http://drops.dagstuhl.de/opus/volltexte/2019/10214},
URN = {urn:nbn:de:0030drops102148},
doi = {10.4230/LIPIcs.IPEC.2018.13},
annote = {Keywords: parallel computation, fixedparameter tractability, kernelization}
}
Keywords: 

parallel computation, fixedparameter tractability, kernelization 
Seminar: 

13th International Symposium on Parameterized and Exact Computation (IPEC 2018) 
Issue Date: 

2019 
Date of publication: 

25.01.2019 