93,841 research outputs found
Abelian Primitive Words
We investigate Abelian primitive words, which are words that are not Abelian
powers. We show that unlike classical primitive words, the set of Abelian
primitive words is not context-free. We can determine whether a word is Abelian
primitive in linear time. Also different from classical primitive words, we
find that a word may have more than one Abelian root. We also consider
enumeration problems and the relation to the theory of codes
Finite automata and algebraic extensions of function fields
We give an automata-theoretic description of the algebraic closure of the
rational function field F_q(t) over a finite field, generalizing a result of
Christol. The description takes place within the Hahn-Mal'cev-Neumann field of
"generalized power series" over F_q. Our approach includes a characterization
of well-ordered sets of rational numbers whose base p expansions are generated
by a finite automaton, as well as some techniques for computing in the
algebraic closure; these include an adaptation to positive characteristic of
Newton's algorithm for finding local expansions of plane curves. We also
conjecture a generalization of our results to several variables.Comment: 40 pages; expanded version of math.AC/0110089; v2: refereed version,
includes minor edit
Detecting palindromes, patterns, and borders in regular languages
Given a language L and a nondeterministic finite automaton M, we consider
whether we can determine efficiently (in the size of M) if M accepts at least
one word in L, or infinitely many words. Given that M accepts at least one word
in L, we consider how long a shortest word can be. The languages L that we
examine include the palindromes, the non-palindromes, the k-powers, the
non-k-powers, the powers, the non-powers (also called primitive words), the
words matching a general pattern, the bordered words, and the unbordered words.Comment: Full version of a paper submitted to LATA 2008. This is a new version
with John Loftus added as a co-author and containing new results on
unbordered word
The Magic Number Problem for Subregular Language Families
We investigate the magic number problem, that is, the question whether there
exists a minimal n-state nondeterministic finite automaton (NFA) whose
equivalent minimal deterministic finite automaton (DFA) has alpha states, for
all n and alpha satisfying n less or equal to alpha less or equal to exp(2,n).
A number alpha not satisfying this condition is called a magic number (for n).
It was shown in [11] that no magic numbers exist for general regular languages,
while in [5] trivial and non-trivial magic numbers for unary regular languages
were identified. We obtain similar results for automata accepting subregular
languages like, for example, combinational languages, star-free, prefix-,
suffix-, and infix-closed languages, and prefix-, suffix-, and infix-free
languages, showing that there are only trivial magic numbers, when they exist.
For finite languages we obtain some partial results showing that certain
numbers are non-magic.Comment: In Proceedings DCFS 2010, arXiv:1008.127
Natural Language Processing at the School of Information Studies for Africa
The lack of persons trained in computational linguistic methods is a severe obstacle to making the Internet and computers accessible to people all over the world in their own languages.
The paper discusses the experiences of designing and teaching an introductory course in Natural Language Processing to graduate computer science students at Addis Ababa University, Ethiopia, in order to initiate the education of computational linguists in the Horn of Africa region
- …