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0711.2270
|
Can a Computer Laugh ?
|
cs.CL cs.AI q-bio.NC
|
A computer model of "a sense of humour" suggested previously
[arXiv:0711.2058,0711.2061], relating the humorous effect with a specific
malfunction in information processing, is given in somewhat different
exposition. Psychological aspects of humour are elaborated more thoroughly. The
mechanism of laughter is formulated on the more general level. Detailed
discussion is presented for the higher levels of information processing, which
are responsible for a perception of complex samples of humour. Development of a
sense of humour in the process of evolution is discussed.
|
0711.2444
|
Proof nets for display logic
|
cs.CL
|
This paper explores several extensions of proof nets for the Lambek calculus
in order to handle the different connectives of display logic in a natural way.
The new proof net calculus handles some recent additions to the Lambek
vocabulary such as Galois connections and Grishin interactions. It concludes
with an exploration of the generative capacity of the Lambek-Grishin calculus,
presenting an embedding of lexicalized tree adjoining grammars into the
Lambek-Grishin calculus.
|
0711.2478
|
A Compact Self-organizing Cellular Automata-based Genetic Algorithm
|
cs.NE cs.AI
|
A Genetic Algorithm (GA) is proposed in which each member of the population
can change schemata only with its neighbors according to a rule. The rule
methodology and the neighborhood structure employ elements from the Cellular
Automata (CA) strategies. Each member of the GA population is assigned to a
cell and crossover takes place only between adjacent cells, according to the
predefined rule. Although combinations of CA and GA approaches have appeared
previously, here we rely on the inherent self-organizing features of CA, rather
than on parallelism. This conceptual shift directs us toward the evolution of
compact populations containing only a handful of members. We find that the
resulting algorithm can search the design space more efficiently than
traditional GA strategies due to its ability to exploit mutations within this
compact self-organizing population. Consequently, premature convergence is
avoided and the final results often are more accurate. In order to reinforce
the superior mutation capability, a re-initialization strategy also is
implemented. Ten test functions and two benchmark structural engineering truss
design problems are examined in order to demonstrate the performance of the
method.
|
0711.2501
|
Error Exponents of Erasure/List Decoding Revisited via Moments of
Distance Enumerators
|
cs.IT math.IT
|
The analysis of random coding error exponents pertaining to erasure/list
decoding, due to Forney, is revisited. Instead of using Jensen's inequality as
well as some other inequalities in the derivation, we demonstrate that an
exponentially tight analysis can be carried out by assessing the relevant
moments of a certain distance enumerator. The resulting bound has the following
advantages: (i) it is at least as tight as Forney's bound, (ii) under certain
symmetry conditions associated with the channel and the random coding
distribution, it is simpler than Forney's bound in the sense that it involves
an optimization over one parameter only (rather than two), and (iii) in certain
special cases, like the binary symmetric channel (BSC), the optimum value of
this parameter can be found in closed form, and so, there is no need to conduct
a numerical search. We have not found yet, however, a numerical example where
this new bound is strictly better than Forney's bound. This may provide an
additional evidence to support Forney's conjecture that his bound is tight for
the average code. We believe that the technique we suggest in this paper can be
useful in simplifying, and hopefully also improving, exponential error bounds
in other problem settings as well.
|
0711.2503
|
Sparsity in time-frequency representations
|
math.CA cs.IT math.IT
|
We consider signals and operators in finite dimension which have sparse
time-frequency representations. As main result we show that an $S$-sparse Gabor
representation in $\mathbb{C}^n$ with respect to a random unimodular window can
be recovered by Basis Pursuit with high probability provided that $S\leq
Cn/\log(n)$. Our results are applicable to the channel estimation problem in
wireless communications and they establish the usefulness of a class of
measurement matrices for compressive sensing.
|
0711.2547
|
Interference Alignment on the Deterministic Channel and Application to
Fully Connected AWGN Interference Networks
|
cs.IT math.IT
|
An interference alignment example is constructed for the deterministic
channel model of the $K$ user interference channel. The deterministic channel
example is then translated into the Gaussian setting, creating the first known
example of a fully connected Gaussian $K$ user interference network with single
antenna nodes, real, non-zero and contant channel coefficients, and no
propagation delays where the degrees of freedom outerbound is achieved. An
analogy is drawn between the propagation delay based interference alignment
examples and the deterministic channel model which also allows similar
constructions for the 2 user $X$ channel as well.
|
0711.2615
|
A Biologically Inspired Classifier
|
cs.DB cs.IR
|
We present a method for measuring the distance among records based on the
correlations of data stored in the corresponding database entries. The original
method (F. Bagnoli, A. Berrones and F. Franci. Physica A 332 (2004) 509-518)
was formulated in the context of opinion formation. The opinions expressed over
a set of topic originate a ``knowledge network'' among individuals, where two
individuals are nearer the more similar their expressed opinions are. Assuming
that individuals' opinions are stored in a database, the authors show that it
is possible to anticipate an opinion using the correlations in the database.
This corresponds to approximating the overlap between the tastes of two
individuals with the correlations of their expressed opinions.
In this paper we extend this model to nonlinear matching functions, inspired
by biological problems such as microarray (probe-sample pairing). We
investigate numerically the error between the correlation and the overlap
matrix for eight sequences of reference with random probes. Results show that
this method is particularly robust for detecting similarities in the presence
of translocations.
|
0711.2642
|
Multiuser MIMO Achievable Rates with Downlink Training and Channel State
Feedback
|
cs.IT math.IT
|
We consider a MIMO fading broadcast channel and compute achievable ergodic
rates when channel state information is acquired at the receivers via downlink
training and it is provided to the transmitter by channel state feedback.
Unquantized (analog) and quantized (digital) channel state feedback schemes are
analyzed and compared under various assumptions. Digital feedback is shown to
be potentially superior when the feedback channel uses per channel state
coefficient is larger than 1. Also, we show that by proper design of the
digital feedback link, errors in the feedback have a minor effect even if
simple uncoded modulation is used on the feedback channel. We discuss first the
case of an unfaded AWGN feedback channel with orthogonal access and then the
case of fading MIMO multi-access (MIMO-MAC). We show that by exploiting the
MIMO-MAC nature of the uplink channel, a much better scaling of the feedback
channel resource with the number of base station antennas can be achieved.
Finally, for the case of delayed feedback, we show that in the realistic case
where the fading process has (normalized) maximum Doppler frequency shift 0 < F
< 1/2, a fraction 1 - 2F of the optimal multiplexing gain is achievable. The
general conclusion of this work is that very significant downlink throughput is
achievable with simple and efficient channel state feedback, provided that the
feedback link is properly designed.
|
0711.2652
|
An information-theoretic analog of a result of Perelman
|
math.DG cs.IT math.IT
|
Each compact manifold M of finite dimension k is differentiable and supports
an intrinsic probability measure. There then exists a measurable transformation
of M to the k-dimensional "surface" of the (k+1)-dimensional ball.
|
0711.2666
|
The Generalized Asymptotic Equipartition Property: Necessary and
Sufficient Conditions
|
cs.IT math.IT
|
Suppose a string $X_1^n=(X_1,X_2,...,X_n)$ generated by a memoryless source
$(X_n)_{n\geq 1}$ with distribution $P$ is to be compressed with distortion no
greater than $D\geq 0$, using a memoryless random codebook with distribution
$Q$. The compression performance is determined by the ``generalized asymptotic
equipartition property'' (AEP), which states that the probability of finding a
$D$-close match between $X_1^n$ and any given codeword $Y_1^n$, is
approximately $2^{-n R(P,Q,D)}$, where the rate function $R(P,Q,D)$ can be
expressed as an infimum of relative entropies. The main purpose here is to
remove various restrictive assumptions on the validity of this result that have
appeared in the recent literature. Necessary and sufficient conditions for the
generalized AEP are provided in the general setting of abstract alphabets and
unbounded distortion measures. All possible distortion levels $D\geq 0$ are
considered; the source $(X_n)_{n\geq 1}$ can be stationary and ergodic; and the
codebook distribution can have memory. Moreover, the behavior of the matching
probability is precisely characterized, even when the generalized AEP is not
valid. Natural characterizations of the rate function $R(P,Q,D)$ are
established under equally general conditions.
|
0711.2712
|
Parity Forwarding for Multiple-Relay Networks
|
cs.IT math.IT
|
This paper proposes a relaying strategy for the multiple-relay network in
which each relay decodes a selection of transmitted messages by other
transmitting terminals, and forwards parities of the decoded codewords. This
protocol improves the previously known achievable rate of the
decode-and-forward (DF) strategy for multirelay networks by allowing relays to
decode only a selection of messages from relays with strong links to it. Hence,
each relay may have several choices as to which messages to decode, and for a
given network many different parity forwarding protocols may exist. A tree
structure is devised to characterize a class of parity forwarding protocols for
an arbitrary multirelay network. Based on this tree structure, closed-form
expressions for the achievable rates of these DF schemes are derived. It is
shown that parity forwarding is capacity achieving for new forms of degraded
relay networks.
|
0711.2745
|
On Capacity Scaling in Arbitrary Wireless Networks
|
cs.IT math.IT
|
In recent work, Ozgur, Leveque, and Tse (2007) obtained a complete scaling
characterization of throughput scaling for random extended wireless networks
(i.e., $n$ nodes are placed uniformly at random in a square region of area
$n$). They showed that for small path-loss exponents $\alpha\in(2,3]$
cooperative communication is order optimal, and for large path-loss exponents
$\alpha > 3$ multi-hop communication is order optimal. However, their results
(both the communication scheme and the proof technique) are strongly dependent
on the regularity induced with high probability by the random node placement.
In this paper, we consider the problem of characterizing the throughput
scaling in extended wireless networks with arbitrary node placement. As a main
result, we propose a more general novel cooperative communication scheme that
works for arbitrarily placed nodes. For small path-loss exponents $\alpha \in
(2,3]$, we show that our scheme is order optimal for all node placements, and
achieves exactly the same throughput scaling as in Ozgur et al. This shows that
the regularity of the node placement does not affect the scaling of the
achievable rates for $\alpha\in (2,3]$. The situation is, however, markedly
different for large path-loss exponents $\alpha >3$. We show that in this
regime the scaling of the achievable per-node rates depends crucially on the
regularity of the node placement. We then present a family of schemes that
smoothly "interpolate" between multi-hop and cooperative communication,
depending upon the level of regularity in the node placement. We establish
order optimality of these schemes under adversarial node placement for $\alpha
> 3$.
|
0711.2762
|
Variations on Information Embedding in Multiple Access and Broadcast
Channels
|
cs.IT math.IT
|
Information embedding (IE) is the transmission of information within a host
signal subject to a distortion constraint. There are two types of embedding
methods, namely irreversible IE and reversible IE, depending upon whether or
not the host, as well as the message, is recovered at the decoder. In
irreversible IE, only the embedded message is recovered at the decoder, and in
reversible IE, both the message and the host are recovered at the decoder. This
paper considers combinations of irreversible and reversible IE in multiple
access channels (MAC) and physically degraded broadcast channels (BC).
|
0711.2801
|
Inverse Sampling for Nonasymptotic Sequential Estimation of Bounded
Variable Means
|
math.ST cs.LG math.PR stat.TH
|
In this paper, we consider the nonasymptotic sequential estimation of means
of random variables bounded in between zero and one. We have rigorously
demonstrated that, in order to guarantee prescribed relative precision and
confidence level, it suffices to continue sampling until the sample sum is no
less than a certain bound and then take the average of samples as an estimate
for the mean of the bounded random variable. We have developed an explicit
formula and a bisection search method for the determination of such bound of
sample sum, without any knowledge of the bounded variable. Moreover, we have
derived bounds for the distribution of sample size. In the special case of
Bernoulli random variables, we have established analytical and numerical
methods to further reduce the bound of sample sum and thus improve the
efficiency of sampling. Furthermore, the fallacy of existing results are
detected and analyzed.
|
0711.2824
|
Degrees of Freedom of Wireless X Networks
|
cs.IT math.IT
|
We explore the degrees of freedom of $M\times N$ user wireless $X$ networks,
i.e. networks of $M$ transmitters and $N$ receivers where every transmitter has
an independent message for every receiver. We derive a general outerbound on
the degrees of freedom \emph{region} of these networks. When all nodes have a
single antenna and all channel coefficients vary in time or frequency, we show
that the \emph{total} number of degrees of freedom of the $X$ network is equal
to $\frac{MN}{M+N-1}$ per orthogonal time and frequency dimension.
Achievability is proved by constructing interference alignment schemes for $X$
networks that can come arbitrarily close to the outerbound on degrees of
freedom. For the case where either M=2 or N=2 we find that the outerbound is
exactly achievable. While $X$ networks have significant degrees of freedom
benefits over interference networks when the number of users is small, our
results show that as the number of users increases, this advantage disappears.
Thus, for large $K$, the $K\times K$ user wireless $X$ network loses half the
degrees of freedom relative to the $K\times K$ MIMO outerbound achievable
through full cooperation. Interestingly, when there are few transmitters
sending to many receivers ($N\gg M$) or many transmitters sending to few
receivers ($M\gg N$), $X$ networks are able to approach the $\min(M,N)$ degrees
of freedom possible with full cooperation on the $M\times N$ MIMO channel.
Similar to the interference channel, we also construct an example of a 2 user
$X$ channel with propagation delays where the outerbound on degrees of freedom
is achieved through interference alignment based on a simple TDMA strategy.
|
0711.2832
|
Premi\`ere \'etape vers une navigation r\'ef\'erentielle par l'image
pour l'assistance \`a la conception des ambiances lumineuses
|
cs.IR
|
In the first design stage, image reference plays a double role of means of
formulation and resolution of problems. In our approach, we consider image
reference as a support of creation activity to generate ideas and we propose a
tool for navigation in references by image in order to assist daylight ambience
design. Within this paper, we present, in a first part, the semantic indexation
method to be used for the indexation of our image database. In a second part we
propose a synthetic analysis of various modes of referential navigation in
order to propose a tool implementing all or a part of these modes.
|
0711.2867
|
Maximizing PageRank via outlinks
|
cs.IR math.RA
|
We analyze linkage strategies for a set I of webpages for which the webmaster
wants to maximize the sum of Google's PageRank scores. The webmaster can only
choose the hyperlinks starting from the webpages of I and has no control on the
hyperlinks from other webpages. We provide an optimal linkage strategy under
some reasonable assumptions.
|
0711.2873
|
Trellis Computations
|
cs.IT math.IT
|
For a certain class of functions, the distribution of the function values can
be calculated in the trellis or a sub-trellis. The forward/backward recursion
known from the BCJR algorithm is generalized to compute the moments of these
distributions. In analogy to the symbol probabilities, by introducing a
constraint at a certain depth in the trellis we obtain symbol moments. These
moments are required for an efficient implementation of the discriminated
belief propagation algorithm in [2], and can furthermore be utilized to compute
conditional entropies in the trellis.
The moment computation algorithm has the same asymptotic complexity as the
BCJR algorithm. It is applicable to any commutative semi-ring, thus actually
providing a generalization of the Viterbi algorithm.
|
0711.2897
|
Estimation of fuzzy anomalies in Water Distribution Systems
|
cs.NE
|
State estimation is necessary in diagnosing anomalies in Water Demand Systems
(WDS). In this paper we present a neural network performing such a task. State
estimation is performed by using optimization, which tries to reconcile all the
available information. Quantification of the uncertainty of the input data
(telemetry measures and demand predictions) can be achieved by means of robust
estate estimation. Using a mathematical model of the network, fuzzy estimated
states for anomalous states of the network can be obtained. They are used to
train a neural network capable of assessing WDS anomalies associated with
particular sets of measurements.
|
0711.2909
|
Comparing the notions of optimality in CP-nets, strategic games and soft
constraints
|
cs.AI cs.GT
|
The notion of optimality naturally arises in many areas of applied
mathematics and computer science concerned with decision making. Here we
consider this notion in the context of three formalisms used for different
purposes in reasoning about multi-agent systems: strategic games, CP-nets, and
soft constraints. To relate the notions of optimality in these formalisms we
introduce a natural qualitative modification of the notion of a strategic game.
We show then that the optimal outcomes of a CP-net are exactly the Nash
equilibria of such games. This allows us to use the techniques of game theory
to search for optimal outcomes of CP-nets and vice-versa, to use techniques
developed for CP-nets to search for Nash equilibria of the considered games.
Then, we relate the notion of optimality used in the area of soft constraints
to that used in a generalization of strategic games, called graphical games. In
particular we prove that for a natural class of soft constraints that includes
weighted constraints every optimal solution is both a Nash equilibrium and
Pareto efficient joint strategy. For a natural mapping in the other direction
we show that Pareto efficient joint strategies coincide with the optimal
solutions of soft constraints.
|
0711.2914
|
Image Classification Using SVMs: One-against-One Vs One-against-All
|
cs.LG cs.AI cs.CV
|
Support Vector Machines (SVMs) are a relatively new supervised classification
technique to the land cover mapping community. They have their roots in
Statistical Learning Theory and have gained prominence because they are robust,
accurate and are effective even when using a small training sample. By their
nature SVMs are essentially binary classifiers, however, they can be adopted to
handle the multiple classification tasks common in remote sensing studies. The
two approaches commonly used are the One-Against-One (1A1) and One-Against-All
(1AA) techniques. In this paper, these approaches are evaluated in as far as
their impact and implication for land cover mapping. The main finding from this
research is that whereas the 1AA technique is more predisposed to yielding
unclassified and mixed pixels, the resulting classification accuracy is not
significantly different from 1A1 approach. It is the authors conclusion
therefore that ultimately the choice of technique adopted boils down to
personal preference and the uniqueness of the dataset at hand.
|
0711.2917
|
Use of Wikipedia Categories in Entity Ranking
|
cs.IR
|
Wikipedia is a useful source of knowledge that has many applications in
language processing and knowledge representation. The Wikipedia category graph
can be compared with the class hierarchy in an ontology; it has some
characteristics in common as well as some differences. In this paper, we
present our approach for answering entity ranking queries from the Wikipedia.
In particular, we explore how to make use of Wikipedia categories to improve
entity ranking effectiveness. Our experiments show that using categories of
example entities works significantly better than using loosely defined target
categories.
|
0711.2961
|
Recognizing Members of the Tournament Equilibrium Set is NP-hard
|
cs.CC cs.GT cs.MA
|
A recurring theme in the mathematical social sciences is how to select the
"most desirable" elements given a binary dominance relation on a set of
alternatives. Schwartz's tournament equilibrium set (TEQ) ranks among the most
intriguing, but also among the most enigmatic, tournament solutions that have
been proposed so far in this context. Due to its unwieldy recursive definition,
little is known about TEQ. In particular, its monotonicity remains an open
problem up to date. Yet, if TEQ were to satisfy monotonicity, it would be a
very attractive tournament solution concept refining both the Banks set and
Dutta's minimal covering set. We show that the problem of deciding whether a
given alternative is contained in TEQ is NP-hard.
|
0711.3077
|
On Low Complexity Maximum Likelihood Decoding of Convolutional Codes
|
cs.IT cs.CC math.IT
|
This paper considers the average complexity of maximum likelihood (ML)
decoding of convolutional codes. ML decoding can be modeled as finding the most
probable path taken through a Markov graph. Integrated with the Viterbi
algorithm (VA), complexity reduction methods such as the sphere decoder often
use the sum log likelihood (SLL) of a Markov path as a bound to disprove the
optimality of other Markov path sets and to consequently avoid exhaustive path
search. In this paper, it is shown that SLL-based optimality tests are
inefficient if one fixes the coding memory and takes the codeword length to
infinity. Alternatively, optimality of a source symbol at a given time index
can be testified using bounds derived from log likelihoods of the neighboring
symbols. It is demonstrated that such neighboring log likelihood (NLL)-based
optimality tests, whose efficiency does not depend on the codeword length, can
bring significant complexity reduction to ML decoding of convolutional codes.
The results are generalized to ML sequence detection in a class of
discrete-time hidden Markov systems.
|
0711.3128
|
Entity Ranking in Wikipedia
|
cs.IR
|
The traditional entity extraction problem lies in the ability of extracting
named entities from plain text using natural language processing techniques and
intensive training from large document collections. Examples of named entities
include organisations, people, locations, or dates. There are many research
activities involving named entities; we are interested in entity ranking in the
field of information retrieval. In this paper, we describe our approach to
identifying and ranking entities from the INEX Wikipedia document collection.
Wikipedia offers a number of interesting features for entity identification and
ranking that we first introduce. We then describe the principles and the
architecture of our entity ranking system, and introduce our methodology for
evaluation. Our preliminary results show that the use of categories and the
link structure of Wikipedia, together with entity examples, can significantly
improve retrieval effectiveness.
|
0711.3152
|
Multipath Channels of Bounded Capacity
|
cs.IT math.IT
|
The capacity of discrete-time, non-coherent, multipath fading channels is
considered. It is shown that if the delay spread is large in the sense that the
variances of the path gains do not decay faster than geometrically, then
capacity is bounded in the signal-to-noise ratio.
|
0711.3176
|
To Decode the Interference or To Consider it as Noise
|
cs.IT math.IT
|
We address single-user data transmission over a channel where the received
signal incurs interference from a finite number of users (interfering users)
that use single codebooks for transmitting their own messages. The receiver,
however, is allowed to decode interfering users' messages. This means the
signal transmitted from any interfering user is either decoded or considered as
noise at the receiver side. We propose the following method to obtain an
achievable rate for this channel. Assuming its own data is decoded
successfully, the receiver partitions the set of interfering users into two
disjoint subsets, namely the set of decodable users and the set of
non-decodable users. Then the transmitter's rate is chosen such that the
intended signal can be jointly decoded with the set of decodable users. To show
the strength of this method, we prove that for the additive Gaussian channel
with Gaussian interfering users, the Gaussian distribution is optimal and the
achievable rate is the capacity of this channel. To obtain the maximum
achievable rate, one needs to find the maximum decodable subset of interfering
users. Due to the large number of possible choices, having efficient algorithms
that find the set of decodable users with maximum cardinality is desired. To
this end, we propose an algorithm that enables the receiver to accomplish this
task in polynomial time.
|
0711.3197
|
How to realize "a sense of humour" in computers ?
|
cs.CL cs.AI q-bio.NC
|
Computer model of a "sense of humour" suggested previously [arXiv:0711.2058,
0711.2061, 0711.2270] is raised to the level of a realistic algorithm.
|
0711.3205
|
Relay Subset Selection in Wireless Networks Using Partial
Decode-and-Forward Transmission
|
cs.IT math.IT
|
This paper considers the problem of selecting a subset of nodes in a two-hop
wireless network to act as relays in aiding the communication between the
source-destination pair. Optimal relay subset selection with the objective of
maximizing the overall throughput is a difficult problem that depends on
multiple factors including node locations, queue lengths and power consumption.
A partial decode-and-forward strategy is applied in this paper to improve the
tractability of the relay selection problem and performance of the overall
network.
Note that the number of relays selected ultimately determines the performance
of the network. This paper benchmarks this performance by determining the net
diversity achieved using the relays selected and the partial decode-and-forward
strategy. This framework is subsequently used to further transform relay
selection into a simpler relay placement problem, and two proximity-based
approximation algorithms are developed to determine the appropriate set of
relays to be selected in the network. Other selection strategies such as random
relay selection and a greedy algorithm that relies on channel state information
are also presented. This paper concludes by showing that the proposed
proximity-based relay selection strategies yield near-optimal expected rates
for a small number of selected relays.
|
0711.3235
|
A Game-Theoretic Analysis of Updating Sets of Probabilities
|
cs.AI math.ST stat.TH
|
We consider how an agent should update her uncertainty when it is represented
by a set $\P$ of probability distributions and the agent observes that a random
variable $X$ takes on value $x$, given that the agent makes decisions using the
minimax criterion, perhaps the best-studied and most commonly-used criterion in
the literature. We adopt a game-theoretic framework, where the agent plays
against a bookie, who chooses some distribution from $\P$. We consider two
reasonable games that differ in what the bookie knows when he makes his choice.
Anomalies that have been observed before, like time inconsistency, can be
understood as arising important because different games are being played,
against bookies with different information. We characterize the important
special cases in which the optimal decision rules according to the minimax
criterion amount to either conditioning or simply ignoring the information.
Finally, we consider the relationship between conditioning and calibration when
uncertainty is described by sets of probabilities.
|
0711.3251
|
Limited Feedback-based Block Diagonalization for the MIMO Broadcast
Channel
|
cs.IT math.IT
|
Block diagonalization is a linear precoding technique for the multiple
antenna broadcast (downlink) channel that involves transmission of multiple
data streams to each receiver such that no multi-user interference is
experienced at any of the receivers. This low-complexity scheme operates only a
few dB away from capacity but requires very accurate channel knowledge at the
transmitter. We consider a limited feedback system where each receiver knows
its channel perfectly, but the transmitter is only provided with a finite
number of channel feedback bits from each receiver. Using a random quantization
argument, we quantify the throughput loss due to imperfect channel knowledge as
a function of the feedback level. The quality of channel knowledge must improve
proportional to the SNR in order to prevent interference-limitations, and we
show that scaling the number of feedback bits linearly with the system SNR is
sufficient to maintain a bounded rate loss. Finally, we compare our
quantization strategy to an analog feedback scheme and show the superiority of
quantized feedback.
|
0711.3338
|
Bounds for Compression in Streaming Models
|
cs.IT math.IT
|
Compression algorithms and streaming algorithms are both powerful tools for
dealing with massive data sets, but many of the best compression algorithms --
e.g., those based on the Burrows-Wheeler Transform -- at first seem
incompatible with streaming. In this paper we consider several popular
streaming models and ask in which, if any, we can compress as well as we can
with the BWT. We first prove a nearly tight tradeoff between memory and
redundancy for the Standard, Multipass and W-Streams models, demonstrating a
bound that is achievable with the BWT but unachievable in those models. We then
show we can compute the related Schindler Transform in the StreamSort model and
the BWT in the Read-Write model and, thus, achieve that bound.
|
0711.3375
|
An Inflationary Fixed Point Operator in XQuery
|
cs.DB
|
We introduce a controlled form of recursion in XQuery, inflationary fixed
points, familiar in the context of relational databases. This imposes
restrictions on the expressible types of recursion, but we show that
inflationary fixed points nevertheless are sufficiently versatile to capture a
wide range of interesting use cases, including the semantics of Regular XPath
and its core transitive closure construct.
While the optimization of general user-defined recursive functions in XQuery
appears elusive, we will describe how inflationary fixed points can be
efficiently evaluated, provided that the recursive XQuery expressions exhibit a
distributivity property. We show how distributivity can be assessed both,
syntactically and algebraically, and provide experimental evidence that XQuery
processors can substantially benefit during inflationary fixed point
evaluation.
|
0711.3412
|
Morphological annotation of Korean with Directly Maintainable Resources
|
cs.CL
|
This article describes an exclusively resource-based method of morphological
annotation of written Korean text. Korean is an agglutinative language. Our
annotator is designed to process text before the operation of a syntactic
parser. In its present state, it annotates one-stem words only. The output is a
graph of morphemes annotated with accurate linguistic information. The
granularity of the tagset is 3 to 5 times higher than usual tagsets. A
comparison with a reference annotated corpus showed that it achieves 89% recall
without any corpus training. The language resources used by the system are
lexicons of stems, transducers of suffixes and transducers of generation of
allomorphs. All can be easily updated, which allows users to control the
evolution of the performances of the system. It has been claimed that
morphological annotation of Korean text could only be performed by a
morphological analysis module accessing a lexicon of morphemes. We show that it
can also be performed directly with a lexicon of words and without applying
morphological rules at annotation time, which speeds up annotation to 1,210
word/s. The lexicon of words is obtained from the maintainable language
resources through a fully automated compilation process.
|
0711.3419
|
Translating OWL and Semantic Web Rules into Prolog: Moving Toward
Description Logic Programs
|
cs.AI
|
To appear in Theory and Practice of Logic Programming (TPLP), 2008.
We are researching the interaction between the rule and the ontology layers
of the Semantic Web, by comparing two options: 1) using OWL and its rule
extension SWRL to develop an integrated ontology/rule language, and 2) layering
rules on top of an ontology with RuleML and OWL. Toward this end, we are
developing the SWORIER system, which enables efficient automated reasoning on
ontologies and rules, by translating all of them into Prolog and adding a set
of general rules that properly capture the semantics of OWL. We have also
enabled the user to make dynamic changes on the fly, at run time. This work
addresses several of the concerns expressed in previous work, such as negation,
complementary classes, disjunctive heads, and cardinality, and it discusses
alternative approaches for dealing with inconsistencies in the knowledge base.
In addition, for efficiency, we implemented techniques called
extensionalization, avoiding reanalysis, and code minimization.
|
0711.3449
|
Lexicon management and standard formats
|
cs.CL
|
International standards for lexicon formats are in preparation. To a certain
extent, the proposed formats converge with prior results of standardization
projects. However, their adequacy for (i) lexicon management and (ii)
lexicon-driven applications have been little debated in the past, nor are they
as a part of the present standardization effort. We examine these issues. IGM
has developed XML formats compatible with the emerging international standards,
and we report experimental results on large-coverage lexica.
|
0711.3452
|
In memoriam Maurice Gross
|
cs.CL
|
Maurice Gross (1934-2001) was both a great linguist and a pioneer in natural
language processing. This article is written in homage to his memory
|
0711.3453
|
A resource-based Korean morphological annotation system
|
cs.CL
|
We describe a resource-based method of morphological annotation of written
Korean text. Korean is an agglutinative language. The output of our system is a
graph of morphemes annotated with accurate linguistic information. The language
resources used by the system can be easily updated, which allows us-ers to
control the evolution of the per-formances of the system. We show that
morphological annotation of Korean text can be performed directly with a
lexicon of words and without morpho-logical rules.
|
0711.3454
|
Graphes param\'etr\'es et outils de lexicalisation
|
cs.CL
|
Shifting to a lexicalized grammar reduces the number of parsing errors and
improves application results. However, such an operation affects a syntactic
parser in all its aspects. One of our research objectives is to design a
realistic model for grammar lexicalization. We carried out experiments for
which we used a grammar with a very simple content and formalism, and a very
informative syntactic lexicon, the lexicon-grammar of French elaborated by the
LADL. Lexicalization was performed by applying the parameterized-graph
approach. Our results tend to show that most information in the lexicon-grammar
can be transferred into a grammar and exploited successfully for the syntactic
parsing of sentences.
|
0711.3457
|
Evaluation of a Grammar of French Determiners
|
cs.CL
|
Existing syntactic grammars of natural languages, even with a far from
complete coverage, are complex objects. Assessments of the quality of parts of
such grammars are useful for the validation of their construction. We evaluated
the quality of a grammar of French determiners that takes the form of a
recursive transition network. The result of the application of this local
grammar gives deeper syntactic information than chunking or information
available in treebanks. We performed the evaluation by comparison with a corpus
independently annotated with information on determiners. We obtained 86%
precision and 92% recall on text not tagged for parts of speech.
|
0711.3545
|
To Code or Not to Code Across Time: Space-Time Coding with Feedback
|
cs.IT math.IT
|
Space-time codes leverage the availability of multiple antennas to enhance
the reliability of communication over wireless channels. While space-time codes
have initially been designed with a focus on open-loop systems, recent
technological advances have enabled the possibility of low-rate feedback from
the receiver to the transmitter. The focus of this paper is on the implications
of this feedback in a single-user multi-antenna system with a general model for
spatial correlation. We assume a limited feedback model, that is, a coherent
receiver and statistics along with B bits of quantized channel information at
the transmitter. We study space-time coding with a family of linear dispersion
(LD) codes that meet an additional orthogonality constraint so as to ensure
low-complexity decoding. Our results show that, when the number of bits of
feedback (B) is small, a space-time coding scheme that is equivalent to
beamforming and does not code across time is optimal in a weak sense in that it
maximizes the average received SNR. As B increases, this weak optimality
transitions to optimality in a strong sense which is characterized by the
maximization of the average mutual information. Thus, from a system designer's
perspective, our work suggests that beamforming may not only be attractive from
a low-complexity viewpoint, but also from an information-theoretic viewpoint.
|
0711.3580
|
An evolutionary model with Turing machines
|
q-bio.QM cs.NE q-bio.GN
|
The development of a large non-coding fraction in eukaryotic DNA and the
phenomenon of the code-bloat in the field of evolutionary computations show a
striking similarity. This seems to suggest that (in the presence of mechanisms
of code growth) the evolution of a complex code can't be attained without
maintaining a large inactive fraction. To test this hypothesis we performed
computer simulations of an evolutionary toy model for Turing machines, studying
the relations among fitness and coding/non-coding ratio while varying mutation
and code growth rates. The results suggest that, in our model, having a large
reservoir of non-coding states constitutes a great (long term) evolutionary
advantage.
|
0711.3591
|
An Estimation of Distribution Algorithm with Intelligent Local Search
for Rule-based Nurse Rostering
|
cs.NE cs.CE
|
This paper proposes a new memetic evolutionary algorithm to achieve explicit
learning in rule-based nurse rostering, which involves applying a set of
heuristic rules for each nurse's assignment. The main framework of the
algorithm is an estimation of distribution algorithm, in which an ant-miner
methodology improves the individual solutions produced in each generation.
Unlike our previous work (where learning is implicit), the learning in the
memetic estimation of distribution algorithm is explicit, i.e. we are able to
identify building blocks directly. The overall approach learns by building a
probabilistic model, i.e. an estimation of the probability distribution of
individual nurse-rule pairs that are used to construct schedules. The local
search processor (i.e. the ant-miner) reinforces nurse-rule pairs that receive
higher rewards. A challenging real world nurse rostering problem is used as the
test problem. Computational results show that the proposed approach outperforms
most existing approaches. It is suggested that the learning methodologies
suggested in this paper may be applied to other scheduling problems where
schedules are built systematically according to specific rules
|
0711.3594
|
Clustering with Transitive Distance and K-Means Duality
|
cs.LG
|
Recent spectral clustering methods are a propular and powerful technique for
data clustering. These methods need to solve the eigenproblem whose
computational complexity is $O(n^3)$, where $n$ is the number of data samples.
In this paper, a non-eigenproblem based clustering method is proposed to deal
with the clustering problem. Its performance is comparable to the spectral
clustering algorithms but it is more efficient with computational complexity
$O(n^2)$. We show that with a transitive distance and an observed property,
called K-means duality, our algorithm can be used to handle data sets with
complex cluster shapes, multi-scale clusters, and noise. Moreover, no
parameters except the number of clusters need to be set in our algorithm.
|
0711.3605
|
Very strict selectional restrictions
|
cs.CL
|
We discuss the characteristics and behaviour of two parallel classes of verbs
in two Romance languages, French and Portuguese. Examples of these verbs are
Port. abater [gado] and Fr. abattre [b\'etail], both meaning "slaughter
[cattle]". In both languages, the definition of the class of verbs includes
several features: - They have only one essential complement, which is a direct
object. - The nominal distribution of the complement is very limited, i.e., few
nouns can be selected as head nouns of the complement. However, this selection
is not restricted to a single noun, as would be the case for verbal idioms such
as Fr. monter la garde "mount guard". - We excluded from the class
constructions which are reductions of more complex constructions, e.g. Port.
afinar [instrumento] com "tune [instrument] with".
|
0711.3628
|
A Perl Package and an Alignment Tool for Phylogenetic Networks
|
q-bio.PE cs.CE
|
Phylogenetic networks are a generalization of phylogenetic trees that allow
for the representation of evolutionary events acting at the population level,
like recombination between genes, hybridization between lineages, and lateral
gene transfer. While most phylogenetics tools implement a wide range of
algorithms on phylogenetic trees, there exist only a few applications to work
with phylogenetic networks, and there are no open-source libraries either.
In order to improve this situation, we have developed a Perl package that
relies on the BioPerl bundle and implements many algorithms on phylogenetic
networks. We have also developed a Java applet that makes use of the
aforementioned Perl package and allows the user to make simple experiments with
phylogenetic networks without having to develop a program or Perl script by
herself.
The Perl package has been accepted as part of the BioPerl bundle. It can be
downloaded from http://dmi.uib.es/~gcardona/BioInfo/Bio-PhyloNetwork.tgz. The
web-based application is available at http://dmi.uib.es/~gcardona/BioInfo/. The
Perl package includes full documentation of all its features.
|
0711.3629
|
Convolutional codes from units in matrix and group rings
|
cs.IT math.IT math.RA
|
A general method for constructing convolutional codes from units in Laurent
series over matrix rings is presented. Using group ring as matrix rings, this
forms a basis for in-depth exploration of convolutional codes from group ring
encoding, wherein the ring in the group ring is itself a group ring. The method
is used to algebraically construct series of convolutional codes. Algebraic
methods are used to compute free distances and to construct convolutional codes
to prescribed distances.
|
0711.3675
|
Derivations of Normalized Mutual Information in Binary Classifications
|
cs.LG cs.IT math.IT
|
This correspondence studies the basic problem of classifications - how to
evaluate different classifiers. Although the conventional performance indexes,
such as accuracy, are commonly used in classifier selection or evaluation,
information-based criteria, such as mutual information, are becoming popular in
feature/model selections. In this work, we propose to assess classifiers in
terms of normalized mutual information (NI), which is novel and well defined in
a compact range for classifier evaluation. We derive close-form relations of
normalized mutual information with respect to accuracy, precision, and recall
in binary classifications. By exploring the relations among them, we reveal
that NI is actually a set of nonlinear functions, with a concordant
power-exponent form, to each performance index. The relations can also be
expressed with respect to precision and recall, or to false alarm and hitting
rate (recall).
|
0711.3691
|
Outilex, plate-forme logicielle de traitement de textes \'ecrits
|
cs.CL
|
The Outilex software platform, which will be made available to research,
development and industry, comprises software components implementing all the
fundamental operations of written text processing: processing without lexicons,
exploitation of lexicons and grammars, language resource management. All data
are structured in XML formats, and also in more compact formats, either
readable or binary, whenever necessary; the required format converters are
included in the platform; the grammar formats allow for combining statistical
approaches with resource-based approaches. Manually constructed lexicons for
French and English, originating from the LADL, and of substantial coverage,
will be distributed with the platform under LGPL-LR license.
|
0711.3726
|
Let's get the student into the driver's seat
|
cs.CL
|
Speaking a language and achieving proficiency in another one is a highly
complex process which requires the acquisition of various kinds of knowledge
and skills, like the learning of words, rules and patterns and their connection
to communicative goals (intentions), the usual starting point. To help the
learner to acquire these skills we propose an enhanced, electronic version of
an age old method: pattern drills (henceforth PDs). While being highly regarded
in the fifties, PDs have become unpopular since then, partially because of
their lack of grounding (natural context) and rigidity. Despite these
shortcomings we do believe in the virtues of this approach, at least with
regard to the acquisition of basic linguistic reflexes or skills (automatisms),
necessary to survive in the new language. Of course, the method needs
improvement, and we will show here how this can be achieved. Unlike tapes or
books, computers are open media, allowing for dynamic changes, taking users'
performances and preferences into account. Building an electronic version of
PDs amounts to building an open resource, accomodatable to the users' ever
changing needs.
|
0711.3856
|
Forward estimation for ergodic time series
|
math.PR cs.IT math.IT
|
The forward estimation problem for stationary and ergodic time series
$\{X_n\}_{n=0}^{\infty}$ taking values from a finite alphabet ${\cal X}$ is to
estimate the probability that $X_{n+1}=x$ based on the observations $X_i$,
$0\le i\le n$ without prior knowledge of the distribution of the process
$\{X_n\}$. We present a simple procedure $g_n$ which is evaluated on the data
segment $(X_0,...,X_n)$ and for which, ${\rm error}(n) = |g_{n}(x)-P(X_{n+1}=x
|X_0,...,X_n)|\to 0$ almost surely for a subclass of all stationary and ergodic
time series, while for the full class the Cesaro average of the error tends to
zero almost surely and moreover, the error tends to zero in probability.
|
0711.3867
|
A Family of Likelihood Ascent Search Multiuser Detectors: Approach to
Single-User Performance via Quasi-Large Random Sequence CDMA
|
cs.IT math.IT
|
Since Tse and Verdu proved that the global maximum likelihood (GML) detector
achieves unit asymptotic multiuser efficiency (AME) in the limit of large
random spreading (LRS) CDMA, no suboptimal detector has been found to achieve
unit AME. In this letter, we obtain that the WSLAS detector with a linear
per-bit complexity achieves unit AME in the LRS-CDMA with a channel load < 1/2
- 1/(4ln2) bits/s/Hz. For a practical system with any user number, a quasi
LRS-CDMA is then proposed to approach the single-user performance in the high
SNR regime.
|
0711.3869
|
A Family of Likelihood Ascent Search Multiuser Detectors: an Upper Bound
of Bit Error Rate and a Lower Bound of Asymptotic Multiuser Efficiency
|
cs.IT math.IT
|
In this paper, the bit error performance of a family of likelihood ascent
search (LAS) multiuser detectors is analyzed. An upper bound on the BER of any
LAS detector is obtained by bounding the fixed point region with the worst
initial detector. The concept of indecomposable errors developed by Verdu is
applied to tighten the upper bound. In a special instance, the upper bound is
reduced to that for all the local maximum likelihood detectors. The upper bound
is comparable with that of the optimum detector obtained by Verdu. A lower
bound on the asymptotic multiuser efficiency (AME) is then obtained. It is
shown that there are nontrivial CDMA channels such that a LAS detector can
achieve unit AME regardless of user number. The AME lower bound provides a
means for further seeking a good set of spreading sequences and power
distribution for spectral and power efficient CDMA.
|
0711.3915
|
Distributed Consensus Algorithms in Sensor Networks: Link Failures and
Channel Noise
|
cs.IT cs.MA math.IT math.OC
|
The paper studies average consensus with random topologies (intermittent
links)
\emph{and} noisy channels. Consensus with noise in the network links leads to
the bias-variance dilemma--running consensus for long reduces the bias of the
final average estimate but increases its variance. We present two different
compromises to this tradeoff: the $\mathcal{A-ND}$ algorithm modifies
conventional consensus by forcing the weights to satisfy a \emph{persistence}
condition (slowly decaying to zero); and the $\mathcal{A-NC}$ algorithm where
the weights are constant but consensus is run for a fixed number of iterations
$\hat{\imath}$, then it is restarted and rerun for a total of $\hat{p}$ runs,
and at the end averages the final states of the $\hat{p}$ runs (Monte Carlo
averaging). We use controlled Markov processes and stochastic approximation
arguments to prove almost sure convergence of $\mathcal{A-ND}$ to the desired
average (asymptotic unbiasedness) and compute explicitly the m.s.e. (variance)
of the consensus limit. We show that $\mathcal{A-ND}$ represents the best of
both worlds--low bias and low variance--at the cost of a slow convergence rate;
rescaling the weights...
|
0711.3926
|
Rateless codes for AVC models
|
cs.IT math.IT
|
The arbitrarily varying channel (AVC) is a channel model whose state is
selected maliciously by an adversary. Fixed-blocklength coding assumes a
worst-case bound on the adversary's capabilities, which leads to pessimistic
results. This paper defines a variable-length perspective on this problem, for
which achievable rates are shown that depend on the realized actions of the
adversary. Specifically, rateless codes are constructed which require a limited
amount of common randomness. These codes are constructed for two kinds of AVC
models. In the first the channel state cannot depend on the channel input, and
in the second it can. As a byproduct, the randomized coding capacity of the AVC
with state depending on the transmitted codeword is found and shown to be
achievable with a small amount of common randomness. The results for this model
are proved using a randomized strategy based on list decoding.
|
0711.3935
|
Coding for Network Coding
|
cs.IT cs.NI math.IT
|
We consider communication over a noisy network under randomized linear
network coding. Possible error mechanism include node- or link- failures,
Byzantine behavior of nodes, or an over-estimate of the network min-cut.
Building on the work of Koetter and Kschischang, we introduce a probabilistic
model for errors. We compute the capacity of this channel and we define an
error-correction scheme based on random sparse graphs and a low-complexity
decoding algorithm. By optimizing over the code degree profile, we show that
this construction achieves the channel capacity in complexity which is jointly
quadratic in the number of coded information bits and sublogarithmic in the
error probability.
|
0711.3964
|
Iterative Filtering for a Dynamical Reputation System
|
cs.IR
|
The paper introduces a novel iterative method that assigns a reputation to n
+ m items: n raters and m objects. Each rater evaluates a subset of objects
leading to a n x m rating matrix with a certain sparsity pattern. From this
rating matrix we give a nonlinear formula to define the reputation of raters
and objects. We also provide an iterative algorithm that superlinearly
converges to the unique vector of reputations and this for any rating matrix.
In contrast to classical outliers detection, no evaluation is discarded in this
method but each one is taken into account with different weights for the
reputation of the objects. The complexity of one iteration step is linear in
the number of evaluations, making our algorithm efficient for large data set.
Experiments show good robustness of the reputation of the objects against
cheaters and spammers and good detection properties of cheaters and spammers.
|
0711.3983
|
Self-dual, dual-containing and related quantum codes from group rings
|
cs.IT math.IT math.RA
|
Classes of self-dual codes and dual-containing codes are constructed. The
codes are obtained within group rings and, using an isomorphism between group
rings and matrices, equivalent codes are obtained in matrix form. Distances and
other properties are derived by working within the group ring. Quantum codes
are constructed from the dual-containing codes.
|
0711.4075
|
Evaluating the Impact of Information Distortion on Normalized
Compression Distance
|
cs.IT math.IT
|
In this paper we apply different techniques of information distortion on a
set of classical books written in English. We study the impact that these
distortions have upon the Kolmogorov complexity and the clustering by
compression technique (the latter based on Normalized Compression Distance,
NCD). We show how to decrease the complexity of the considered books
introducing several modifications in them. We measure how the information
contained in each book is maintained using a clustering error measure. We find
experimentally that the best way to keep the clustering error is by means of
modifications in the most frequent words. We explain the details of these
information distortions and we compare with other kinds of modifications like
random word distortions and unfrequent word distortions. Finally, some
phenomenological explanations from the different empirical results that have
been carried out are presented.
|
0711.4142
|
Content Reuse and Interest Sharing in Tagging Communities
|
cs.DL cs.IR
|
Tagging communities represent a subclass of a broader class of user-generated
content-sharing online communities. In such communities users introduce and tag
content for later use. Although recent studies advocate and attempt to harness
social knowledge in this context by exploiting collaboration among users,
little research has been done to quantify the current level of user
collaboration in these communities. This paper introduces two metrics to
quantify the level of collaboration: content reuse and shared interest. Using
these two metrics, this paper shows that the current level of collaboration in
CiteULike and Connotea is consistently low, which significantly limits the
potential of harnessing the social knowledge in communities. This study also
discusses implications of these findings in the context of recommendation and
reputation systems.
|
0711.4175
|
Graph Entropy, Network Coding and Guessing games
|
math.CO cs.IT math.IT
|
We introduce the (private) entropy of a directed graph (in a new network
coding sense) as well as a number of related concepts. We show that the entropy
of a directed graph is identical to its guessing number and can be bounded from
below with the number of vertices minus the size of the graph's shortest index
code. We show that the Network Coding solvability of each specific multiple
unicast network is completely determined by the entropy (as well as by the
shortest index code) of the directed graph that occur by identifying each
source node with each corresponding target node.
Shannon's information inequalities can be used to calculate upper bounds on a
graph's entropy as well as calculating the size of the minimal index code.
Recently, a number of new families of so-called non-shannon-type information
inequalities have been discovered. It has been shown that there exist
communication networks with a capacity strictly less than required for
solvability, but where this fact cannot be derived using Shannon's classical
information inequalities. Based on this result we show that there exist graphs
with an entropy that cannot be calculated using only Shannon's classical
information inequalities, and show that better estimate can be obtained by use
of certain non-shannon-type information inequalities.
|
0711.4309
|
Knowware: the third star after Hardware and Software
|
cs.SE cs.AI cs.CY
|
This book proposes to separate knowledge from software and to make it a
commodity that is called knowware. The architecture, representation and
function of Knowware are discussed. The principles of knowware engineering and
its three life cycle models: furnace model, crystallization model and spiral
model are proposed and analyzed. Techniques of software/knowware co-engineering
are introduced. A software component whose knowledge is replaced by knowware is
called mixware. An object and component oriented development schema of mixware
is introduced. In particular, the tower model and ladder model for mixware
development are proposed and discussed. Finally, knowledge service and knowware
based Web service are introduced and compared with Web service. In summary,
knowware, software and hardware should be considered as three equally important
underpinnings of IT industry.
Ruqian Lu is a professor of computer science of the Institute of Mathematics,
Academy of Mathematics and System Sciences. He is a fellow of Chinese Academy
of Sciences. His research interests include artificial intelligence, knowledge
engineering and knowledge based software engineering. He has published more
than 100 papers and 10 books. He has won two first class awards from the
Academia Sinica and a National second class prize from the Ministry of Science
and Technology. He has also won the sixth Hua Loo-keng Mathematics Prize.
|
0711.4324
|
Report on "American Option Pricing and Hedging Strategies"
|
cs.CE cs.DM
|
This paper mainly discusses the American option's hedging strategies via
binomialmodel and the basic idea of pricing and hedging American option.
Although the essential scheme of hedging is almost the same as European option,
small differences may arise when simulating the process for American option
holder has more rights, spelling that the option can be exercised at anytime
before its maturity. Our method is dynamic-hedging method.
|
0711.4380
|
Randomness and metastability in CDMA paradigms
|
cs.IT math.IT
|
Code Division Multiple Access (CDMA) in which the signature code assignment
to users contains a random element has recently become a cornerstone of CDMA
research. The random element in the construction is particularly attractive in
that it provides robustness and flexibility in application, whilst not making
significant sacrifices in terms of multiuser efficiency. We present results for
sparse random codes of two types, with and without modulation. Simple
microscopic consideration on system samples would suggest differences in the
phase space of the two models, but we demonstrate that the thermodynamic
results and metastable states are equivalent in the minimum bit error rate
detector. We analyse marginal properties of interactions and also make
analogies to constraint satisfiability problems in order to understand
qualitative features of detection and metastable states. This may have
consequences for developing algorithmic methods to escape metastable states,
thus improving decoding performance.
|
0711.4388
|
Contextual Information Retrieval based on Algorithmic Information Theory
and Statistical Outlier Detection
|
cs.IR cs.IT math.IT
|
The main contribution of this paper is to design an Information Retrieval
(IR) technique based on Algorithmic Information Theory (using the Normalized
Compression Distance- NCD), statistical techniques (outliers), and novel
organization of data base structure. The paper shows how they can be integrated
to retrieve information from generic databases using long (text-based) queries.
Two important problems are analyzed in the paper. On the one hand, how to
detect "false positives" when the distance among the documents is very low and
there is actual similarity. On the other hand, we propose a way to structure a
document database which similarities distance estimation depends on the length
of the selected text. Finally, the experimental evaluations that have been
carried out to study previous problems are shown.
|
0711.4406
|
Optimization of Information Rate Upper and Lower Bounds for Channels
with Memory
|
cs.IT math.IT
|
We consider the problem of minimizing upper bounds and maximizing lower
bounds on information rates of stationary and ergodic discrete-time channels
with memory. The channels we consider can have a finite number of states, such
as partial response channels, or they can have an infinite state-space, such as
time-varying fading channels. We optimize recently-proposed information rate
bounds for such channels, which make use of auxiliary finite-state machine
channels (FSMCs). Our main contribution in this paper is to provide iterative
expectation-maximization (EM) type algorithms to optimize the parameters of the
auxiliary FSMC to tighten these bounds. We provide an explicit, iterative
algorithm that improves the upper bound at each iteration. We also provide an
effective method for iteratively optimizing the lower bound. To demonstrate the
effectiveness of our algorithms, we provide several examples of partial
response and fading channels, where the proposed optimization techniques
significantly tighten the initial upper and lower bounds. Finally, we compare
our results with an improved variation of the \emph{simplex} local optimization
algorithm, called \emph{Soblex}. This comparison shows that our proposed
algorithms are superior to the Soblex method, both in terms of robustness in
finding the tightest bounds and in computational efficiency. Interestingly,
from a channel coding/decoding perspective, optimizing the lower bound is
related to increasing the achievable mismatched information rate, i.e., the
information rate of a communication system where the decoder at the receiver is
matched to the auxiliary channel, and not to the original channel.
|
0711.4414
|
Exploiting Multi-Antennas for Opportunistic Spectrum Sharing in
Cognitive Radio Networks
|
cs.IT math.IT
|
In cognitive radio (CR) networks, there are scenarios where the secondary
(lower priority) users intend to communicate with each other by
opportunistically utilizing the transmit spectrum originally allocated to the
existing primary (higher priority) users. For such a scenario, a secondary user
usually has to trade off between two conflicting goals at the same time: one is
to maximize its own transmit throughput; and the other is to minimize the
amount of interference it produces at each primary receiver. In this paper, we
study this fundamental tradeoff from an information-theoretic perspective by
characterizing the secondary user's channel capacity under both its own
transmit-power constraint as well as a set of interference-power constraints
each imposed at one of the primary receivers. In particular, this paper
exploits multi-antennas at the secondary transmitter to effectively balance
between spatial multiplexing for the secondary transmission and interference
avoidance at the primary receivers. Convex optimization techniques are used to
design algorithms for the optimal secondary transmit spatial spectrum that
achieves the capacity of the secondary transmission. Suboptimal solutions for
ease of implementation are also presented and their performances are compared
with the optimal solution. Furthermore, algorithms developed for the
single-channel transmission are also extended to the case of multi-channel
transmission whereby the secondary user is able to achieve opportunistic
spectrum sharing via transmit adaptations not only in space, but in time and
frequency domains as well.
|
0711.4444
|
Building the Tangent and Adjoint codes of the Ocean General Circulation
Model OPA with the Automatic Differentiation tool TAPENADE
|
cs.MS cs.CE
|
The ocean general circulation model OPA is developed by the LODYC team at
Paris VI university. OPA has recently undergone a major rewriting, migrating to
FORTRAN95, and its adjoint code needs to be rebuilt. For earlier versions, the
adjoint of OPA was written by hand at a high development cost. We use the
Automatic Differentiation tool TAPENADE to build mechanicaly the tangent and
adjoint codes of OPA. We validate the differentiated codes by comparison with
divided differences, and also with an identical twin experiment. We apply
state-of-the-art methods to improve the performance of the adjoint code. In
particular we implement the Griewank and Walther's binomial checkpointing
algorithm which gives us an optimal trade-off between time and memory
consumption. We apply a specific strategy to differentiate the iterative linear
solver that comes from the implicit time stepping scheme
|
0711.4452
|
Covariance and PCA for Categorical Variables
|
cs.LG
|
Covariances from categorical variables are defined using a regular simplex
expression for categories. The method follows the variance definition by Gini,
and it gives the covariance as a solution of simultaneous equations. The
calculated results give reasonable values for test data. A method of principal
component analysis (RS-PCA) is also proposed using regular simplex expressions,
which allows easy interpretation of the principal components. The proposed
methods apply to variable selection problem of categorical data USCensus1990
data. The proposed methods give appropriate criterion for the variable
selection problem of categorical
|
0711.4475
|
Valence extraction using EM selection and co-occurrence matrices
|
cs.CL
|
This paper discusses two new procedures for extracting verb valences from raw
texts, with an application to the Polish language. The first novel technique,
the EM selection algorithm, performs unsupervised disambiguation of valence
frame forests, obtained by applying a non-probabilistic deep grammar parser and
some post-processing to the text. The second new idea concerns filtering of
incorrect frames detected in the parsed text and is motivated by an observation
that verbs which take similar arguments tend to have similar frames. This
phenomenon is described in terms of newly introduced co-occurrence matrices.
Using co-occurrence matrices, we split filtering into two steps. The list of
valid arguments is first determined for each verb, whereas the pattern
according to which the arguments are combined into frames is computed in the
following stage. Our best extracted dictionary reaches an $F$-score of 45%,
compared to an $F$-score of 39% for the standard frame-based BHT filtering.
|
0711.4507
|
The Second Law as a Cause of the Evolution
|
cs.IT cs.AI math.IT
|
It is a common belief that in any environment where life is possible, life
will be generated. Here it is suggested that the cause for a spontaneous
generation of complex systems is probability driven processes. Based on
equilibrium thermodynamics, it is argued that in low occupation number
statistical systems, the second law of thermodynamics yields an increase of
thermal entropy and a canonic energy distribution. However, in high occupation
number statistical systems, the same law for the same reasons yields an
increase of information and a Benford's law/power-law energy distribution. It
is therefore, plausible, that eventually the heat death is not necessarily the
end of the universe.
|
0711.4508
|
Representation and Measure of Structural Information
|
cs.CC cs.CV cs.IT math.IT
|
We introduce a uniform representation of general objects that captures the
regularities with respect to their structure. It allows a representation of a
general class of objects including geometric patterns and images in a sparse,
modular, hierarchical, and recursive manner. The representation can exploit any
computable regularity in objects to compactly describe them, while also being
capable of representing random objects as raw data. A set of rules uniformly
dictates the interpretation of the representation into raw signal, which makes
it possible to ask what pattern a given raw signal contains. Also, it allows
simple separation of the information that we wish to ignore from that which we
measure, by using a set of maps to delineate the a priori parts of the objects,
leaving only the information in the structure.
Using the representation, we introduce a measure of information in general
objects relative to structures defined by the set of maps. We point out that
the common prescription of encoding objects by strings to use Kolmogorov
complexity is meaningless when, as often is the case, the encoding is not
specified in any way other than that it exists. Noting this, we define the
measure directly in terms of the structures of the spaces in which the objects
reside. As a result, the measure is defined relative to a set of maps that
characterize the structures. It turns out that the measure is equivalent to
Kolmogorov complexity when it is defined relative to the maps characterizing
the structure of natural numbers. Thus, the formulation gives the larger class
of objects a meaningful measure of information that generalizes Kolmogorov
complexity.
|
0711.4557
|
On Outage Behavior of Wideband Slow-Fading Channels
|
cs.IT math.IT
|
This paper investigates point-to-point information transmission over a
wideband slow-fading channel, modeled as an (asymptotically) large number of
independent identically distributed parallel channels, with the random channel
fading realizations remaining constant over the entire coding block. On the one
hand, in the wideband limit the minimum achievable energy per nat required for
reliable transmission, as a random variable, converges in probability to
certain deterministic quantity. On the other hand, the exponential decay rate
of the outage probability, termed as the wideband outage exponent,
characterizes how the number of parallel channels, {\it i.e.}, the
``bandwidth'', should asymptotically scale in order to achieve a target outage
probability at a target energy per nat. We examine two scenarios: when the
transmitter has no channel state information and adopts uniform transmit power
allocation among parallel channels; and when the transmitter is endowed with an
one-bit channel state feedback for each parallel channel and accordingly
allocates its transmit power. For both scenarios, we evaluate the wideband
minimum energy per nat and the wideband outage exponent, and discuss their
implication for system performance.
|
0711.4603
|
A Note on Quantum Hamming Bound
|
quant-ph cs.IT math.IT
|
Proving the quantum Hamming bound for degenerate nonbinary stabilizer codes
has been an open problem for a decade. In this note, I prove this bound for
double error-correcting degenerate stabilizer codes. Also, I compute the
maximum length of single and double error-correcting MDS stabilizer codes over
finite fields.
|
0711.4759
|
Copeland Voting Fully Resists Constructive Control
|
cs.GT cs.CC cs.MA
|
Control and bribery are settings in which an external agent seeks to
influence the outcome of an election. Faliszewski et al. [FHHR07] proved that
Llull voting (which is here denoted by Copeland^1) and a variant (here denoted
by Copeland^0) of Copeland voting are computationally resistant to many, yet
not all, types of constructive control and that they also provide broad
resistance to bribery. We study a parameterized version of Copeland voting,
denoted by Copeland^alpha where the parameter alpha is a rational number
between 0 and 1 that specifies how ties are valued in the pairwise comparisons
of candidates in Copeland elections. We establish resistance or vulnerability
results, in every previously studied control scenario, for Copeland^alpha, for
each rational alpha, 0 <alpha < 1. In particular, we prove that Copeland^0.5,
the system commonly referred to as ``Copeland voting,'' provides full
resistance to constructive control. Among the systems with a polynomial-time
winner problem, this is the first natural election system proven to have full
resistance to constructive control. Results on bribery and fixed-parameter
tractability of bounded-case control proven for Copeland^0 and Copeland^1 in
[FHHR07] are extended to Copeland^alpha for each rational alpha, 0 < alpha < 1;
we also give results in more flexible models such as microbribery and extended
control.
|
0711.4792
|
On the Capacity of a Class of MIMO Cognitive Radios
|
cs.IT math.IT
|
Cognitive radios have been studied recently as a means to utilize spectrum in
a more efficient manner. This paper focuses on the fundamental limits of
operation of a MIMO cognitive radio network with a single licensed user and a
single cognitive user. The channel setting is equivalent to an interference
channel with degraded message sets (with the cognitive user having access to
the licensed user's message). An achievable region and an outer bound is
derived for such a network setting. It is shown that under certain conditions,
the achievable region is optimal for a portion of the capacity region that
includes sum capacity.
|
0711.4809
|
Local independence of fractional Brownian motion
|
math.PR cs.IT math.IT
|
Let S(t,t') be the sigma-algebra generated by the differences X(s)-X(s) with
s,s' in the interval(t,t'), where (X_t) is the fractional Brownian motion
process with Hurst index H between 0 and 1. We prove that for any two distinct
t and t' the sigma-algebras S(t-a,t+a) and S(t'-a,t'+a) are asymptotically
independent as a tends to 0. We show this in the strong sense that Shannon's
mutual information between these two sigma-algebras tends to zero as a tends to
0. Some generalizations and quantitative estimates are provided also.
|
0711.4864
|
Cooperative Relaying with State Available at the Relay
|
cs.IT math.IT
|
We consider a state-dependent full-duplex relay channel with the state of the
channel non-causally available at only the relay. In the framework of
cooperative wireless networks, some specific terminals can be equipped with
cognition capabilities, i.e, the relay in our model. In the discrete memoryless
(DM) case, we derive lower and upper bounds on channel capacity. The lower
bound is obtained by a coding scheme at the relay that consists in a
combination of codeword splitting, Gel'fand-Pinsker binning, and a
decode-and-forward scheme. The upper bound is better than that obtained by
assuming that the channel state is available at the source and the destination
as well. For the Gaussian case, we also derive lower and upper bounds on
channel capacity. The lower bound is obtained by a coding scheme which is based
on a combination of codeword splitting and Generalized dirty paper coding. The
upper bound is also better than that obtained by assuming that the channel
state is available at the source, the relay, and the destination. The two
bounds meet, and so give the capacity, in some special cases for the degraded
Gaussian case.
|
0711.4902
|
Circumspect descent prevails in solving random constraint satisfaction
problems
|
cs.DS cond-mat.stat-mech cs.AI
|
We study the performance of stochastic local search algorithms for random
instances of the $K$-satisfiability ($K$-SAT) problem. We introduce a new
stochastic local search algorithm, ChainSAT, which moves in the energy
landscape of a problem instance by {\em never going upwards} in energy.
ChainSAT is a \emph{focused} algorithm in the sense that it considers only
variables occurring in unsatisfied clauses. We show by extensive numerical
investigations that ChainSAT and other focused algorithms solve large $K$-SAT
instances almost surely in linear time, up to high clause-to-variable ratios
$\alpha$; for example, for K=4 we observe linear-time performance well beyond
the recently postulated clustering and condensation transitions in the solution
space. The performance of ChainSAT is a surprise given that by design the
algorithm gets trapped into the first local energy minimum it encounters, yet
no such minima are encountered. We also study the geometry of the solution
space as accessed by stochastic local search algorithms.
|
0711.4924
|
Nonuniform Bribery
|
cs.GT cs.CC cs.MA
|
We study the concept of bribery in the situation where voters are willing to
change their votes as we ask them, but where their prices depend on the nature
of the change we request. Our model is an extension of the one of Faliszewski
et al. [FHH06], where each voter has a single price for any change we may ask
for. We show polynomial-time algorithms for our version of bribery for a broad
range of voting protocols, including plurality, veto, approval, and utility
based voting. In addition to our polynomial-time algorithms we provide
NP-completeness results for a couple of our nonuniform bribery problems for
weighted voters, and a couple of approximation algorithms for NP-complete
bribery problems defined in [FHH06] (in particular, an FPTAS for
plurality-weighted-$bribery problem).
|
0712.0042
|
On the Mutual Information Distribution of OFDM-Based Spatial
Multiplexing: Exact Variance and Outage Approximation
|
cs.IT math.IT
|
This paper considers the distribution of the mutual information of
frequency-selective spatially-uncorrelated Rayleigh fading MIMO channels.
Results are presented for OFDM-based spatial multiplexing. New exact
closed-form expressions are derived for the variance of the mutual information.
In contrast to previous results, our new expressions apply for systems with
both arbitrary numbers of antennas and arbitrary-length channels. Simplified
expressions are also presented for high and low SNR regimes. The analytical
variance results are used to provide accurate analytical approximations for the
distribution of the mutual information and the outage capacity.
|
0712.0057
|
On Precision - Redundancy Relation in the Design of Source Coding
Algorithms
|
cs.IT math.IT
|
We study the effects of finite-precision representation of source's
probabilities on the efficiency of classic source coding algorithms, such as
Shannon, Gilbert-Moore, or arithmetic codes. In particular, we establish the
following simple connection between the redundancy $R$ and the number of bits
$W$ necessary for representation of source's probabilities in computer's memory
($R$ is assumed to be small): \begin{equation*} W \lesssim \eta \log_2
\frac{m}{R}, \end{equation*} where $m$ is the cardinality of the source's
alphabet, and $\eta \leqslant 1$ is an implementation-specific constant. In
case of binary alphabets ($m=2$) we show that there exist codes for which $\eta
= 1/2$, and in $m$-ary case ($m > 2$) we show that there exist codes for which
$\eta = m/(m+1)$. In general case, however (which includes designs relying on
progressive updates of frequency counters), we show that $\eta = 1$. Usefulness
of these results for practical designs of source coding algorithms is also
discussed.
|
0712.0097
|
Redundancy Estimates for Word-Based Encoding of Sequences Produced by a
Bernoulli Source
|
cs.IT math.IT
|
The efficiency of a code is estimated by its redundancy $R$, while the
complexity of a code is estimated by its average delay $\bar N$. In this work
we construct word-based codes, for which $R \lesssim \bar N^{-5/3}$. Therefore,
word-based codes can attain the same redundancy as block-codes while being much
less complex.
We also consider uniform on the output codes, the benefit of which is the
lack of a running synchronization error. For such codes $\bar N^{-1} \lesssim R
\lesssim \bar N^{-1}$, except for a case when all input symbols are
equiprobable, when $R \leqslant \bar N^{-2}$ for infinitely many $\bar N$.
|
0712.0105
|
On estimating the memory for finitarily Markovian processes
|
math.PR cs.IT math.IT
|
Finitarily Markovian processes are those processes
$\{X_n\}_{n=-\infty}^{\infty}$ for which there is a finite $K$ ($K =
K(\{X_n\}_{n=-\infty}^0$) such that the conditional distribution of $X_1$ given
the entire past is equal to the conditional distribution of $X_1$ given only
$\{X_n\}_{n=1-K}^0$. The least such value of $K$ is called the memory length.
We give a rather complete analysis of the problems of universally estimating
the least such value of $K$, both in the backward sense that we have just
described and in the forward sense, where one observes successive values of
$\{X_n\}$ for $n \geq 0$ and asks for the least value $K$ such that the
conditional distribution of $X_{n+1}$ given $\{X_i\}_{i=n-K+1}^n$ is the same
as the conditional distribution of $X_{n+1}$ given $\{X_i\}_{i=-\infty}^n$. We
allow for finite or countably infinite alphabet size.
|
0712.0130
|
On the Relationship between the Posterior and Optimal Similarity
|
cs.LG
|
For a classification problem described by the joint density $P(\omega,x)$,
models of $P(\omega\eq\omega'|x,x')$ (the ``Bayesian similarity measure'') have
been shown to be an optimal similarity measure for nearest neighbor
classification. This paper analyzes demonstrates several additional properties
of that conditional distribution. The paper first shows that we can
reconstruct, up to class labels, the class posterior distribution $P(\omega|x)$
given $P(\omega\eq\omega'|x,x')$, gives a procedure for recovering the class
labels, and gives an asymptotically Bayes-optimal classification procedure. It
also shows, given such an optimal similarity measure, how to construct a
classifier that outperforms the nearest neighbor classifier and achieves
Bayes-optimal classification rates. The paper then analyzes Bayesian similarity
in a framework where a classifier faces a number of related classification
tasks (multitask learning) and illustrates that reconstruction of the class
posterior distribution is not possible in general. Finally, the paper
identifies a distinct class of classification problems using
$P(\omega\eq\omega'|x,x')$ and shows that using $P(\omega\eq\omega'|x,x')$ to
solve those problems is the Bayes optimal solution.
|
0712.0131
|
Learning Similarity for Character Recognition and 3D Object Recognition
|
cs.CV
|
I describe an approach to similarity motivated by Bayesian methods. This
yields a similarity function that is learnable using a standard Bayesian
methods. The relationship of the approach to variable kernel and variable
metric methods is discussed. The approach is related to variable kernel
Experimental results on character recognition and 3D object recognition are
presented..
|
0712.0136
|
Learning View Generalization Functions
|
cs.CV
|
Learning object models from views in 3D visual object recognition is usually
formulated either as a function approximation problem of a function describing
the view-manifold of an object, or as that of learning a class-conditional
density. This paper describes an alternative framework for learning in visual
object recognition, that of learning the view-generalization function. Using
the view-generalization function, an observer can perform Bayes-optimal 3D
object recognition given one or more 2D training views directly, without the
need for a separate model acquisition step. The paper shows that view
generalization functions can be computationally practical by restating two
widely-used methods, the eigenspace and linear combination of views approaches,
in a view generalization framework. The paper relates the approach to recent
methods for object recognition based on non-uniform blurring. The paper
presents results both on simulated 3D ``paperclip'' objects and real-world
images from the COIL-100 database showing that useful view-generalization
functions can be realistically be learned from a comparatively small number of
training examples.
|
0712.0137
|
View Based Methods can achieve Bayes-Optimal 3D Recognition
|
cs.CV
|
This paper proves that visual object recognition systems using only 2D
Euclidean similarity measurements to compare object views against previously
seen views can achieve the same recognition performance as observers having
access to all coordinate information and able of using arbitrary 3D models
internally. Furthermore, it demonstrates that such systems do not require more
training views than Bayes-optimal 3D model-based systems. For building computer
vision systems, these results imply that using view-based or appearance-based
techniques with carefully constructed combination of evidence mechanisms may
not be at a disadvantage relative to 3D model-based systems. For computational
approaches to human vision, they show that it is impossible to distinguish
view-based and 3D model-based techniques for 3D object recognition solely by
comparing the performance achievable by human and 3D model-based systems.}
|
0712.0171
|
A Spectral Approach to Analyzing Belief Propagation for 3-Coloring
|
cs.CC cs.AI cs.DM
|
Contributing to the rigorous understanding of BP, in this paper we relate the
convergence of BP to spectral properties of the graph. This encompasses a
result for random graphs with a ``planted'' solution; thus, we obtain the first
rigorous result on BP for graph coloring in the case of a complex graphical
structure (as opposed to trees). In particular, the analysis shows how Belief
Propagation breaks the symmetry between the $3!$ possible permutations of the
color classes.
|
0712.0271
|
Distributed Arithmetic Coding for the Asymmetric Slepian-Wolf problem
|
cs.IT math.IT
|
Distributed source coding schemes are typically based on the use of channels
codes as source codes. In this paper we propose a new paradigm, termed
"distributed arithmetic coding", which exploits the fact that arithmetic codes
are good source as well as channel codes. In particular, we propose a
distributed binary arithmetic coder for Slepian-Wolf coding with decoder side
information, along with a soft joint decoder. The proposed scheme provides
several advantages over existing Slepian-Wolf coders, especially its good
performance at small block lengths, and the ability to incorporate arbitrary
source models in the encoding process, e.g. context-based statistical models.
We have compared the performance of distributed arithmetic coding with turbo
codes and low-density parity-check codes, and found that the proposed approach
has very competitive performance.
|
0712.0305
|
The analytic computability of the Shannon transform for a large class of
random matrix channels
|
cs.IT math.IT
|
We define a class of "algebraic" random matrix channels for which one can
generically compute the limiting Shannon transform using numerical techniques
and often enumerate the low SNR series expansion coefficients in closed form.
We describe this class, the coefficient enumeration techniques and compare
theory with simulations.
|
0712.0392
|
Collaborative Gain in Resource Sharing Communication Networks
|
cs.IT math.IT
|
This paper has been withdrawn
|
0712.0451
|
A Reactive Tabu Search Algorithm for Stimuli Generation in
Psycholinguistics
|
cs.AI cs.CC cs.DM cs.LG
|
The generation of meaningless "words" matching certain statistical and/or
linguistic criteria is frequently needed for experimental purposes in
Psycholinguistics. Such stimuli receive the name of pseudowords or nonwords in
the Cognitive Neuroscience literatue. The process for building nonwords
sometimes has to be based on linguistic units such as syllables or morphemes,
resulting in a numerical explosion of combinations when the size of the
nonwords is increased. In this paper, a reactive tabu search scheme is proposed
to generate nonwords of variables size. The approach builds pseudowords by
using a modified Metaheuristic algorithm based on a local search procedure
enhanced by a feedback-based scheme. Experimental results show that the new
algorithm is a practical and effective tool for nonword generation.
|
0712.0499
|
Simrank++: Query rewriting through link analysis of the click graph
|
cs.DL cs.DB cs.IR
|
We focus on the problem of query rewriting for sponsored search. We base
rewrites on a historical click graph that records the ads that have been
clicked on in response to past user queries. Given a query q, we first consider
Simrank as a way to identify queries similar to q, i.e., queries whose ads a
user may be interested in. We argue that Simrank fails to properly identify
query similarities in our application, and we present two enhanced version of
Simrank: one that exploits weights on click graph edges and another that
exploits ``evidence.'' We experimentally evaluate our new schemes against
Simrank, using actual click graphs and queries form Yahoo!, and using a variety
of metrics. Our results show that the enhanced methods can yield more and
better query rewrites.
|
0712.0541
|
New Construction of A Family of Quasi-Twisted Two-Weight Codes
|
cs.IT math.IT
|
Based on cyclic and consta-cyclic simplex codes, a new explicit construction
of a family of two-weight codes is presented. These two-weight codes obtained
are in the form of 2-generator quasi-cyclic, or quasi-twisted structure. Based
on this construction, new optimal binary quasi-cyclic [195, 8, 96], [210, 8,
104] and [240, 8, 120] codes, and good QC ternary [208, 6, 135] and [221, 6,
144] codes are thus obtained. It is also shown that many codes among the family
meet the Griesmer bound and thereful are optimal.
|
0712.0653
|
Equations of States in Singular Statistical Estimation
|
cs.LG
|
Learning machines which have hierarchical structures or hidden variables are
singular statistical models because they are nonidentifiable and their Fisher
information matrices are singular. In singular statistical models, neither the
Bayes a posteriori distribution converges to the normal distribution nor the
maximum likelihood estimator satisfies asymptotic normality. This is the main
reason why it has been difficult to predict their generalization performances
from trained states. In this paper, we study four errors, (1) Bayes
generalization error, (2) Bayes training error, (3) Gibbs generalization error,
and (4) Gibbs training error, and prove that there are mathematical relations
among these errors. The formulas proved in this paper are equations of states
in statistical estimation because they hold for any true distribution, any
parametric model, and any a priori distribution. Also we show that Bayes and
Gibbs generalization errors are estimated by Bayes and Gibbs training errors,
and propose widely applicable information criteria which can be applied to both
regular and singular statistical models.
|
0712.0744
|
Computational Chemotaxis in Ants and Bacteria over Dynamic Environments
|
cs.MA cs.AI q-bio.PE q-bio.QM
|
Chemotaxis can be defined as an innate behavioural response by an organism to
a directional stimulus, in which bacteria, and other single-cell or
multicellular organisms direct their movements according to certain chemicals
in their environment. This is important for bacteria to find food (e.g.,
glucose) by swimming towards the highest concentration of food molecules, or to
flee from poisons. Based on self-organized computational approaches and similar
stigmergic concepts we derive a novel swarm intelligent algorithm. What strikes
from these observations is that both eusocial insects as ant colonies and
bacteria have similar natural mechanisms based on stigmergy in order to emerge
coherent and sophisticated patterns of global collective behaviour. Keeping in
mind the above characteristics we will present a simple model to tackle the
collective adaptation of a social swarm based on real ant colony behaviors (SSA
algorithm) for tracking extrema in dynamic environments and highly multimodal
complex functions described in the well-know De Jong test suite. Later, for the
purpose of comparison, a recent model of artificial bacterial foraging (BFOA
algorithm) based on similar stigmergic features is described and analyzed.
Final results indicate that the SSA collective intelligence is able to cope and
quickly adapt to unforeseen situations even when over the same cooperative
foraging period, the community is requested to deal with two different and
contradictory purposes, while outperforming BFOA in adaptive speed. Results
indicate that the present approach deals well in severe Dynamic Optimization
problems.
|
0712.0836
|
Evolving localizations in reaction-diffusion cellular automata
|
cs.AI
|
We consider hexagonal cellular automata with immediate cell neighbourhood and
three cell-states. Every cell calculates its next state depending on the
integral representation of states in its neighbourhood, i.e. how many
neighbours are in each one state. We employ evolutionary algorithms to breed
local transition functions that support mobile localizations (gliders), and
characterize sets of the functions selected in terms of quasi-chemical systems.
Analysis of the set of functions evolved allows to speculate that mobile
localizations are likely to emerge in the quasi-chemical systems with limited
diffusion of one reagent, a small number of molecules is required for
amplification of travelling localizations, and reactions leading to stationary
localizations involve relatively equal amount of quasi-chemical species.
Techniques developed can be applied in cascading signals in nature-inspired
spatially extended computing devices, and phenomenological studies and
classification of non-linear discrete systems.
|
0712.0840
|
A Universal Kernel for Learning Regular Languages
|
cs.LG cs.DM
|
We give a universal kernel that renders all the regular languages linearly
separable. We are not able to compute this kernel efficiently and conjecture
that it is intractable, but we do have an efficient $\eps$-approximation.
|
0712.0871
|
Balancing forward and feedback error correction for erasure channels
with unreliable feedback
|
cs.IT math.IT
|
The traditional information theoretic approach to studying feedback is to
consider ideal instantaneous high-rate feedback of the channel outputs to the
encoder. This was acceptable in classical work because the results were
negative: Shannon pointed out that even perfect feedback often does not improve
capacity and in the context of symmetric DMCs, Dobrushin showed that it does
not improve the fixed block-coding error exponents in the interesting high rate
regime. However, it has recently been shown that perfect feedback does allow
great improvements in the asymptotic tradeoff between end-to-end delay and
probability of error, even for symmetric channels at high rate. Since gains are
claimed with ideal instantaneous feedback, it is natural to wonder whether
these improvements remain if the feedback is unreliable or otherwise limited.
Here, packet-erasure channels are considered on both the forward and feedback
links. First, the feedback channel is considered as a given and a strategy is
given to balance forward and feedback error correction in the suitable
information-theoretic limit of long end-to-end delays. At high enough rates,
perfect-feedback performance is asymptotically attainable despite having only
unreliable feedback! Second, the results are interpreted in the zero- sum case
of "half-duplex" nodes where the allocation of bandwidth or time to the
feedback channel comes at the direct expense of the forward channel. It turns
out that even here, feedback is worthwhile since dramatically lower asymptotic
delays are possible by appropriately balancing forward and feedback error
correction.
The results easily generalize to channels with strictly positive
zero-undeclared-error capacities.
|
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