𝔖 Bobbio Scriptorium
✦   LIBER   ✦

Clifford algebras and approximating the permanent

✍ Scribed by Steve Chien; Lars Rasmussen; Alistair Sinclair


Publisher
Elsevier Science
Year
2003
Tongue
English
Weight
314 KB
Volume
67
Category
Article
ISSN
0022-0000

No coin nor oath required. For personal study only.

✦ Synopsis


We study approximation algorithms for the permanent of an n  n ð0; 1Þ matrix A based on the following simple idea: obtain a random matrix B by replacing each 1-entry of A independently by 7e; where e is a random basis element of a suitable algebra; then output jdetðBÞj 2 : This estimator is always unbiased, but it may have exponentially large variance. In our first main result we show that, if we take the algebra to be a Clifford algebra of dimension polynomial in n; then we get an estimator with small variance. Hence, only a constant number of trials suffices to estimate the permanent to good accuracy. The idea of using Clifford algebras is a natural extension of earlier work by Godsil and Gutman, Karmarkar et al., and Barvinok, who used the real numbers, complex numbers and quaternions, respectively. The above result implies that, in principle, this approach gives a fully-polynomial randomized approximation scheme for the permanent, provided jdetðBÞj 2 can be efficiently computed in the Clifford algebras. Since these algebras are noncommutative it is not clear how to do this. However, our second main result shows how to compute in polynomial time an estimator with the same mean and variance over the 4-dimensional algebra (which is the quaternions, and is non-commutative); in addition to providing some hope that the computations can be performed in higher dimensions, this quaternion algorithm provides an exponential improvement in the variance over that of the 2-dimensional complex version studied by Karmarkar et al.


📜 SIMILAR VOLUMES


Discriminant and Clifford algebras
✍ Anne Quéguiner-Mathieu; Jean-Pierre Tignol 📂 Article 📅 2002 🏛 Springer-Verlag 🌐 French ⚖ 390 KB