A faster hafnian formula for complex matrices and its benchmarking on a supercomputer
Abstract
We introduce new and simple algorithms for the calculation of the number of perfect matchings of complex weighted, undirected graphs with and without loops. Our compact formulas for the hafnian and loop hafnian of $n \times n $ complex matrices run in $O(n^3 2^{n/2})$ time, are embarrassingly parallelizable and, to the best of our knowledge, are the fastest exact algorithms to compute these quantities. Despite our highly optimized algorithm, numerical benchmarks on the Titan supercomputer with matrices up to size $56 \times 56$ indicate that one would require the 288000 CPUs of this machine for about a month and a half to compute the hafnian of a $100 \times 100$ matrix.
 Publication:

arXiv eprints
 Pub Date:
 May 2018
 arXiv:
 arXiv:1805.12498
 Bibcode:
 2018arXiv180512498B
 Keywords:

 Computer Science  Data Structures and Algorithms;
 Quantum Physics
 EPrint:
 11 pages, 7 figures. The source code of the library is available at https://github.com/XanaduAI/hafnian . Accepted for publication in Journal of Experimental Algorithmics