181,226 research outputs found
Short lists with short programs in short time - a short proof
Bauwens, Mahklin, Vereshchagin and Zimand [ECCC TR13-007] and Teutsch
[arxiv:1212.6104] have shown that given a string x it is possible to construct
in polynomial time a list containing a short description of it. We simplify
their technique and present a shorter proof of this result
Linear list-approximation for short programs (or the power of a few random bits)
A -short program for a string is a description of of length at
most , where is the Kolmogorov complexity of . We show that
there exists a randomized algorithm that constructs a list of elements that
contains a -short program for . We also show a polynomial-time
randomized construction that achieves the same list size for -short programs. These results beat the lower bounds shown by Bauwens et al.
\cite{bmvz:c:shortlist} for deterministic constructions of such lists. We also
prove tight lower bounds for the main parameters of our result. The
constructions use only ( for the polynomial-time
result) random bits . Thus using only few random bits it is possible to do
tasks that cannot be done by any deterministic algorithm regardless of its
running time
Short lists for shortest descriptions in short time
Is it possible to find a shortest description for a binary string? The
well-known answer is "no, Kolmogorov complexity is not computable." Faced with
this barrier, one might instead seek a short list of candidates which includes
a laconic description. Remarkably such approximations exist. This paper
presents an efficient algorithm which generates a polynomial-size list
containing an optimal description for a given input string. Along the way, we
employ expander graphs and randomness dispersers to obtain an Explicit Online
Matching Theorem for bipartite graphs and a refinement of Muchnik's Conditional
Complexity Theorem. Our main result extends recent work by Bauwens, Mahklin,
Vereschchagin, and Zimand
Synthesizing Short-Circuiting Validation of Data Structure Invariants
This paper presents incremental verification-validation, a novel approach for
checking rich data structure invariants expressed as separation logic
assertions. Incremental verification-validation combines static verification of
separation properties with efficient, short-circuiting dynamic validation of
arbitrarily rich data constraints. A data structure invariant checker is an
inductive predicate in separation logic with an executable interpretation; a
short-circuiting checker is an invariant checker that stops checking whenever
it detects at run time that an assertion for some sub-structure has been fully
proven statically. At a high level, our approach does two things: it statically
proves the separation properties of data structure invariants using a static
shape analysis in a standard way but then leverages this proof in a novel
manner to synthesize short-circuiting dynamic validation of the data
properties. As a consequence, we enable dynamic validation to make up for
imprecision in sound static analysis while simultaneously leveraging the static
verification to make the remaining dynamic validation efficient. We show
empirically that short-circuiting can yield asymptotic improvements in dynamic
validation, with low overhead over no validation, even in cases where static
verification is incomplete
On approximate decidability of minimal programs
An index in a numbering of partial-recursive functions is called minimal
if every lesser index computes a different function from . Since the 1960's
it has been known that, in any reasonable programming language, no effective
procedure determines whether or not a given index is minimal. We investigate
whether the task of determining minimal indices can be solved in an approximate
sense. Our first question, regarding the set of minimal indices, is whether
there exists an algorithm which can correctly label 1 out of indices as
either minimal or non-minimal. Our second question, regarding the function
which computes minimal indices, is whether one can compute a short list of
candidate indices which includes a minimal index for a given program. We give
some negative results and leave the possibility of positive results as open
questions
PKI Scalability Issues
This report surveys different PKI technologies such as PKIX and SPKI and the
issues of PKI that affect scalability. Much focus is spent on certificate
revocation methodologies and status verification systems such as CRLs,
Delta-CRLs, CRS, Certificate Revocation Trees, Windowed Certificate Revocation,
OCSP, SCVP and DVCS.Comment: 23 pages, 2 figure
Forty hours of declarative programming: Teaching Prolog at the Junior College Utrecht
This paper documents our experience using declarative languages to give
secondary school students a first taste of Computer Science. The course aims to
teach students a bit about programming in Prolog, but also exposes them to
important Computer Science concepts, such as unification or searching
strategies. Using Haskell's Snap Framework in combination with our own
NanoProlog library, we have developed a web application to teach this course.Comment: In Proceedings TFPIE 2012, arXiv:1301.465
Epistemic Protocols for Distributed Gossiping
Gossip protocols aim at arriving, by means of point-to-point or group
communications, at a situation in which all the agents know each other's
secrets. We consider distributed gossip protocols which are expressed by means
of epistemic logic. We provide an operational semantics of such protocols and
set up an appropriate framework to argue about their correctness. Then we
analyze specific protocols for complete graphs and for directed rings.Comment: In Proceedings TARK 2015, arXiv:1606.0729
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