264 research outputs found
Linear and sublinear time algorithms for the basis of abelian groups
AbstractIt is well known that every finite abelian group G can be represented as a direct product of cyclic groups: G≅G1×G2×⋯×Gt, where each Gi is a cyclic group of order pj for some prime p and integer j≥1. If ai generates the cyclic group of Gi, i=1,2,…,t, then the elements a1,a2,…,at are called a basis of G. We show a randomized algorithm such that given a set of generators M={x1,…,xk} for an abelian group G and the prime factorization of order ord(xi)(i=1,…,k), it computes a basis of G in O(|M|(logn)2+∑i=1tnipini/2) time, where n=|G| has prime factorization p1n1p2n2⋯ptnt (which is not a part of input). This generalizes Buchmann and Schmidt’s algorithm that takes O(|M||G|) time. In another model, all elements in an abelian group are put into a list as a part of input. We obtain an O(n) time deterministic algorithm and a sublinear time randomized algorithm for computing a basis of an abelian group
Quantum pattern matching fast on average
The -dimensional pattern matching problem is to find an occurrence of a
pattern of length within a text of length , with . This task models various problems in text and
image processing, among other application areas. This work describes a quantum
algorithm which solves the pattern matching problem for random patterns and
texts in time . For
large this is super-polynomially faster than the best possible classical
algorithm, which requires time . The
algorithm is based on the use of a quantum subroutine for finding hidden shifts
in dimensions, which is a variant of algorithms proposed by Kuperberg.Comment: 22 pages, 2 figures; v3: further minor changes, essentially published
versio
The diameter of random Cayley digraphs of given degree
We consider random Cayley digraphs of order with uniformly distributed
generating set of size . Specifically, we are interested in the asymptotics
of the probability such a Cayley digraph has diameter two as and
. We find a sharp phase transition from 0 to 1 at around . In particular, if is asymptotically linear in , the
probability converges exponentially fast to 1.Comment: 11 page
Learning and Testing Variable Partitions
Let be a multivariate function from a product set to an
Abelian group . A -partition of with cost is a partition of
the set of variables into non-empty subsets such that is -close to
for some with
respect to a given error metric. We study algorithms for agnostically learning
partitions and testing -partitionability over various groups and error
metrics given query access to . In particular we show that
Given a function that has a -partition of cost , a partition
of cost can be learned in time
for any .
In contrast, for and learning a partition of cost is NP-hard.
When is real-valued and the error metric is the 2-norm, a
2-partition of cost can be learned in time
.
When is -valued and the error metric is Hamming
weight, -partitionability is testable with one-sided error and
non-adaptive queries. We also show that even
two-sided testers require queries when .
This work was motivated by reinforcement learning control tasks in which the
set of control variables can be partitioned. The partitioning reduces the task
into multiple lower-dimensional ones that are relatively easier to learn. Our
second algorithm empirically increases the scores attained over previous
heuristic partitioning methods applied in this context.Comment: Innovations in Theoretical Computer Science (ITCS) 202
Explicit universal sampling sets in finite vector spaces
In this paper we construct explicit sampling sets and present reconstruction
algorithms for Fourier signals on finite vector spaces , with for
a suitable prime . The two sets have sizes of order and
respectively, where is the number of large coefficients
in the Fourier transform. The algorithms approximate the function up to a small
constant of the best possible approximation with non-zero Fourier
coefficients. The fastest of the algorithms has complexity
An Efficient Quantum Algorithm for some Instances of the Group Isomorphism Problem
In this paper we consider the problem of testing whether two finite groups
are isomorphic. Whereas the case where both groups are abelian is well
understood and can be solved efficiently, very little is known about the
complexity of isomorphism testing for nonabelian groups. Le Gall has
constructed an efficient classical algorithm for a class of groups
corresponding to one of the most natural ways of constructing nonabelian groups
from abelian groups: the groups that are extensions of an abelian group by
a cyclic group with the order of coprime with . More precisely,
the running time of that algorithm is almost linear in the order of the input
groups. In this paper we present a quantum algorithm solving the same problem
in time polynomial in the logarithm of the order of the input groups. This
algorithm works in the black-box setting and is the first quantum algorithm
solving instances of the nonabelian group isomorphism problem exponentially
faster than the best known classical algorithms.Comment: 20 pages; this is the full version of a paper that will appear in the
Proceedings of the 27th International Symposium on Theoretical Aspects of
Computer Science (STACS 2010
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