This paper analyses the influence of including agents of different degrees of
intelligence in a multiagent system. The goal is to better understand how we
can develop intelligence tests that can evaluate social intelligence. We
analyse several reinforcement algorithms in several contexts of cooperation and
competition. Our experimental setting is inspired by the recently developed
Darwin-Wallace distribution.
In evaluating prediction markets (and other crowd-prediction mechanisms),
investigators have repeatedly observed a so-called "wisdom of crowds" effect,
which roughly says that the average of participants performs much better than
the average participant. The market price---an average or at least aggregate of
traders' beliefs---offers a better estimate than most any individual trader's
opinion. In this paper, we ask a stronger question: how does the market price
compare to the best trader's belief, not just the average trader.
The holistic approach to sustainable urban planning implies using different
models in an integrated way that is capable of simulating the urban system. As
the interconnection of such models is not a trivial task, one of the key
elements that may be applied is the description of the urban geometric
properties in an "interoperable" way.
A resistive memory network that has no crossover wiring is proposed to
overcome the hardware limitations to size and functional complexity that is
associated with conventional analogue neural networks. The proposed memory
network is based on simple network cells that are arranged in a hierarchical
modular architecture. Cognitive functionality of this network is demonstrated
by an example of character recognition. The network is trained by an
evolutionary process to completely recognise characters deformed by random
noise, rotation, scaling and shifting
Dana Scott used the partial order among partial functions for his
mathematical model of recursively defined functions. He interpreted the partial
order as one of information content. In this paper we elaborate on Scott's
suggestion of regarding computation as a process of information maximization by
applying it to the solution of constraint satisfaction problems. Here the
method of constraint propagation can be interpreted as decreasing uncertainty
about the solution -- that is, as gain in information about the solution.
The bi-objective winner determination problem (2WDP-SC) of a combinatorial
procurement auction for transport contracts comes up to a multi-criteria set
covering problem. We are given a set B of bundle bids. A bundle bid b in B
consists of a bidding carrier c_b, a bid price p_b, and a set tau_b of
transport contracts which is a subset of the set T of tendered transport
contracts. Additionally, the transport quality q_t,c_b is given which is
expected to be realized when a transport contract t is executed by a carrier
c_b.
We review some existing methods for the computation of first order moments on
junction trees using Shafer-Shenoy algorithm. First, we consider the problem of
first order moments computation as vertices problem in junction trees. In this
way, the problem is solved using the memory space of an order of the junction
tree edge-set cardinality. After that, we consider two algorithms,
Lauritzen-Nilsson algorithm, and Mau\'a et al.
Covering model provides a general framework for granular computing in that
overlapping among granules are almost indispensable. For any given covering,
both intersection and union of covering blocks containing an element are
exploited as granules to form granular worlds at different abstraction levels,
respectively, and transformations among these different granular worlds are
also discussed.
Until very recently most language research has, in a Cartesian manner,
traditionally regarded linguistic phenomena as internal, mental, isolationist
and amodal (that is, separate and independent from perception, action and
emotion systems, and the body); a view endorsed in psychology, philosophy, and
linguistics.
Hierarchical Task Network (HTN) planning uses task decomposition to plan for
an executable sequence of actions as a solution to a problem. In order to
reason effectively, an HTN planner needs expressive domain knowledge. For
instance, a simplified HTN planning system such as JSHOP2 uses such
expressivity and avoids some task interactions due to the increased complexity
of the planning process.
Temporal networks are ubiquitous and evolve over time by the addition,
deletion, and changing of links, nodes, and attributes. Although many
relational datasets contain temporal information, the majority of existing
techniques in relational learning focus on static snapshots and ignore the
temporal dynamics. We propose a framework for discovering temporal
representations of relational data to increase the accuracy of statistical
relational learning algorithms. The temporal relational representations serve
as a basis for classification, ensembles, and pattern mining in evolving
domains.
In this paper we present the experimental results of the neural network
control of a servo-system in order to control its speed. The control strategy
is implemented by using an inverse-model control based on Artificial Neural
Networks (ANNs). The network training was performed using two learning
algorithms: Levenberg-Marquardt and Bayesian regularization. We evaluate the
generalization capability for each method according to both the correct
operation of the controller to follow the reference signal, and the control
efforts developed by the ANN-based controller.
Trying to be effective (no matter who exactly and in what field) a person
face the problem which inevitably destroys all our attempts to easily get to a
desired goal. The problem is the existence of some insuperable barriers for our
mind, anotherwords barriers for principles of thinking. They are our clue and
main reason for research. Here we investigate these barriers and their features
exposing the nature of mental process. We start from special structures which
reflect the ways to define relations between objects.
The theoretical transition from the graphs of production systems to the
bipartite graphs of the MIVAR nets is shown. Examples of the implementation of
the MIVAR nets in the formalisms of matrixes and graphs are given. The linear
computational complexity of algorithms for automated building of objects and
rules of the MIVAR nets is theoretically proved. On the basis of the MIVAR nets
the UDAV software complex is developed, handling more than 1.17 million objects
and more than 3.5 million rules on ordinary computers.
Evolutionary algorithms (EAs), simulating the evolution process of natural
species, are used to solve optimization problems. Crossover (also called
recombination), originated from simulating the chromosome exchange phenomena in
zoogamy reproduction, is widely employed in EAs to generate offspring
solutions, of which the effectiveness has been examined empirically in
applications. However, due to the irregularity of crossover operators and the
complicated interactions to mutation, crossover operators are hard to analyze
and thus have few theoretical results.
Resolution is the rule of inference at the basis of most procedures for
automated reasoning. In these procedures, the input formula is first translated
into an equisatisfiable formula in conjunctive normal form (CNF) and then
represented as a set of clauses. Deduction starts by inferring new clauses by
resolution, and goes on until the empty clause is generated or satisfiability
of the set of clauses is proven, e.g., because no new clauses can be generated.
This report outlines an approach to learning generative models from data. We
express models as probabilistic programs, which allows us to capture abstract
patterns within the examples. By choosing our language for programs to be an
extension of the algebraic data type of the examples, we can begin with a
program that generates all and only the examples. We then introduce greater
abstraction, and hence generalization, incrementally to the extent that it
improves the posterior probability of the examples given the program.
This paper introduces the SEQ BIN meta-constraint with a polytime algorithm
achieving general- ized arc-consistency according to some properties. SEQ BIN
can be used for encoding counting con- straints such as CHANGE, SMOOTH or
INCREAS- ING NVALUE. For some of these constraints and some of their variants
GAC can be enforced with a time and space complexity linear in the sum of
domain sizes, which improves or equals the best known results of the
literature.
Purpose: In recent years Monte-Carlo sampling methods, such as Monte Carlo
tree search, have achieved tremendous success in model free reinforcement
learning. A combination of the so called upper confidence bounds policy to
preserve the "exploration vs. exploitation" balance to select actions for
sample evaluations together with massive computing power to store and to update
dynamically a rather large pre-evaluated game tree lead to the development of
software that has beaten the top human player in the game of Go on a 9 by 9
board.
This paper presents a novel L1-norm semi-supervised learning algorithm for
robust image analysis by giving new L1-norm formulation of Laplacian
regularization which is the key step of graph-based semi-supervised learning.
Since our L1-norm Laplacian regularization is defined directly over the
eigenvectors of the normalized Laplacian matrix, we successfully formulate
semi-supervised learning as an L1-norm linear reconstruction problem which can
be effectively solved with sparse coding.
This paper applies machine learning and the mathematics of chaos to the task
of designing indoor rock-climbing routes. Chaotic variation has been used to
great advantage on music and dance, but the challenges here are quite
different, beginning with the representation. We present a formalized system
for transcribing rock climbing problems, then describe a variation generator
that is designed to support human route-setters in designing new and
interesting climbing problems.
This paper introduces and analyzes a battery of inference models for the
problem of semantic role labeling: one based on constraint satisfaction, and
several strategies that model the inference as a meta-learning problem using
discriminative classifiers. These classifiers are developed with a rich set of
novel features that encode proposition and sentence-level information. To our
knowledge, this is the first work that: (a) performs a thorough analysis of
learning-based inference models for semantic role labeling, and (b) compares
several inference strategies in this context.
We characterize the search landscape of random instances of the job shop
scheduling problem (JSP). Specifically, we investigate how the expected values
of (1) backbone size, (2) distance between near-optimal schedules, and (3)
makespan of random schedules vary as a function of the job to machine ratio
(N/M). For the limiting cases N/M approaches 0 and N/M approaches infinity we
provide analytical results, while for intermediate values of N/M we perform
experiments. We prove that as N/M approaches 0, backbone size approaches 100%,
while as N/M approaches infinity the backbone vanishes.
We study properties of programs with monotone and convex constraints. We
extend to these formalisms concepts and results from normal logic programming.
They include the notions of strong and uniform equivalence with their
characterizations, tight programs and Fages Lemma, program completion and loop
formulas. Our results provide an abstract account of properties of some recent
extensions of logic programming with aggregates, especially the formalism of
lparse programs.
The Partially Observable Markov Decision Process has long been recognized as
a rich framework for real-world planning and control problems, especially in
robotics. However exact solutions in this framework are typically
computationally intractable for all but the smallest problems. A well-known
technique for speeding up POMDP solving involves performing value backups at
specific belief points, rather than over the entire belief simplex. The
efficiency of this approach, however, depends greatly on the selection of
points.
Efficient representations and solutions for large decision problems with
continuous and discrete variables are among the most important challenges faced
by the designers of automated decision support systems. In this paper, we
describe a novel hybrid factored Markov decision process (MDP) model that
allows for a compact representation of these problems, and a new hybrid
approximate linear programming (HALP) framework that permits their efficient
solutions.
We consider interactive tools that help users search for their most preferred
item in a large collection of options. In particular, we examine
example-critiquing, a technique for enabling users to incrementally construct
preference models by critiquing example options that are presented to them. We
present novel techniques for improving the example-critiquing technology by
adding suggestions to its displayed options. Such suggestions are calculated
based on an analysis of users current preference model and their potential
hidden preferences.
It was recently proved that a sound and complete qualitative simulator does
not exist, that is, as long as the input-output vocabulary of the
state-of-the-art QSIM algorithm is used, there will always be input models
which cause any simulator with a coverage guarantee to make spurious
predictions in its output. In this paper, we examine whether a meaningfully
expressive restriction of this vocabulary is possible so that one can build a
simulator with both the soundness and completeness properties.
Linear Temporal Logic (LTL) is widely used for defining conditions on the
execution paths of dynamic systems. In the case of dynamic systems that allow
for nondeterministic evolutions, one has to specify, along with an LTL formula
f, which are the paths that are required to satisfy the formula. Two extreme
cases are the universal interpretation A.f, which requires that the formula be
satisfied for all execution paths, and the existential interpretation E.f,
which requires that the formula be satisfied for some execution path.
A delta-model is a satisfying assignment of a Boolean formula for which any
small alteration, such as a single bit flip, can be repaired by flips to some
small number of other bits, yielding a new satisfying assignment. These
satisfying assignments represent robust solutions to optimization problems
(e.g., scheduling) where it is possible to recover from unforeseen events
(e.g., a resource becoming unavailable). The concept of delta-models was
introduced by Ginsberg, Parkes and Roy (AAAI 1998), where it was proved that
finding delta-models for general Boolean formulas is NP-complete.
Multimodal conversational interfaces provide a natural means for users to
communicate with computer systems through multiple modalities such as speech
and gesture. To build effective multimodal interfaces, automated interpretation
of user multimodal inputs is important. Inspired by the previous investigation
on cognitive status in multimodal human machine interaction, we have developed
a greedy algorithm for interpreting user referring expressions (i.e.,
multimodal reference resolution).
In recent years, CP-nets have emerged as a useful tool for supporting
preference elicitation, reasoning, and representation. CP-nets capture and
support reasoning with qualitative conditional preference statements,
statements that are relatively natural for users to express. In this paper, we
extend the CP-nets formalism to handle another class of very natural
qualitative statements one often uses in expressing preferences in daily life -
statements of relative importance of attributes.
As partial justification of their framework for iterated belief revision
Darwiche and Pearl convincingly argued against Boutiliers natural revision and
provided a prototypical revision operator that fits into their scheme. We show
that the Darwiche-Pearl arguments lead naturally to the acceptance of a smaller
class of operators which we refer to as admissible.
We present a novel framework for integrating prior knowledge into
discriminative classifiers. Our framework allows discriminative classifiers
such as Support Vector Machines (SVMs) to utilize prior knowledge specified in
the generative setting. The dual objective of fitting the data and respecting
prior knowledge is formulated as a bilevel program, which is solved
(approximately) via iterative application of second-order cone programming.
This article develops Probabilistic Hybrid Action Models (PHAMs), a realistic
causal model for predicting the behavior generated by modern percept-driven
robot plans. PHAMs represent aspects of robot behavior that cannot be
represented by most action models used in AI planning: the temporal structure
of continuous control processes, their non-deterministic effects, several modes
of their interferences, and the achievement of triggering conditions in
closed-loop robot plans.
Multiple sequence alignment (MSA) is a ubiquitous problem in computational
biology. Although it is NP-hard to find an optimal solution for an arbitrary
number of sequences, due to the importance of this problem researchers are
trying to push the limits of exact algorithms further. Since MSA can be cast as
a classical path finding problem, it is attracting a growing number of AI
researchers interested in heuristic search algorithms as a challenge with
actual practical relevance. In this paper, we first review two previous,
complementary lines of research.
In this paper, we introduce DLS-MC, a new stochastic local search algorithm
for the maximum clique problem. DLS-MC alternates between phases of iterative
improvement, during which suitable vertices are added to the current clique,
and plateau search, during which vertices of the current clique are swapped
with vertices not contained in the current clique. The selection of vertices is
solely based on vertex penalties that are dynamically adjusted during the
search, and a perturbation mechanism is used to overcome search stagnation.
In a peer-to-peer inference system, each peer can reason locally but can also
solicit some of its acquaintances, which are peers sharing part of its
vocabulary. In this paper, we consider peer-to-peer inference systems in which
the local theory of each peer is a set of propositional clauses defined upon a
local vocabulary. An important characteristic of peer-to-peer inference systems
is that the global theory (the union of all peer theories) is not known (as
opposed to partition-based reasoning systems).
A non-binary Constraint Satisfaction Problem (CSP) can be solved directly
using extended versions of binary techniques. Alternatively, the non-binary
problem can be translated into an equivalent binary one. In this case, it is
generally accepted that the translated problem can be solved by applying
well-established techniques for binary CSPs. In this paper we evaluate the
applicability of the latter approach.
Between 1998 and 2004, the planning community has seen vast progress in terms
of the sizes of benchmark examples that domain-independent planners can tackle
successfully. The key technique behind this progress is the use of heuristic
functions based on relaxing the planning task at hand, where the relaxation is
to assume that all delete lists are empty. The unprecedented success of such
methods, in many commonly used benchmark examples, calls for an understanding
of what classes of domains these methods are well suited for.
We present a partial-order, conformant, probabilistic planner, Probapop which
competed in the blind track of the Probabilistic Planning Competition in IPC-4.
We explain how we adapt distance based heuristics for use with probabilistic
domains. Probapop also incorporates heuristics based on probability of success.
We explain the successes and difficulties encountered during the design and
implementation of Probapop.
We discuss an attentional model for simultaneous object tracking and
recognition that is driven by gaze data. Motivated by theories of perception,
the model consists of two interacting pathways: identity and control, intended
to mirror the what and where pathways in neuroscience models. The identity
pathway models object appearance and performs classification using deep
(factored)-Restricted Boltzmann Machines. At each point in time the
observations consist of foveated images, with decaying resolution toward the
periphery of the gaze.
In this paper we demonstrate that two common problems in Machine
Learning---imbalanced and overlapping data distributions---do not have
independent effects on the performance of SVM classifiers. This result is
notable since it shows that a model of either of these factors must account for
the presence of the other. Our study of the relationship between these problems
has lead to the discovery of a previously unreported form of "covert"
overfitting which is resilient to commonly used empirical regularization
techniques.
A decision process in which rewards depend on history rather than merely on
the current state is called a decision process with non-Markovian rewards
(NMRDP). In decision-theoretic planning, where many desirable behaviours are
more naturally expressed as properties of execution sequences rather than as
properties of states, NMRDPs form a more natural model than the commonly
adopted fully Markovian decision process (MDP) model.
Code optimization and high level synthesis can be posed as constraint
satisfaction and optimization problems, such as graph coloring used in register
allocation. Graph coloring is also used to model more traditional CSPs relevant
to AI, such as planning, time-tabling and scheduling. Provably optimal
solutions may be desirable for commercial and defense applications.
Additionally, for applications such as register allocation and code
optimization, naturally-occurring instances of graph coloring are often small
and can be solved optimally.
Tabu search is one of the most effective heuristics for locating high-quality
solutions to a diverse array of NP-hard combinatorial optimization problems.
Despite the widespread success of tabu search, researchers have a poor
understanding of many key theoretical aspects of this algorithm, including
models of the high-level run-time dynamics and identification of those search
space features that influence problem difficulty. We consider these questions
in the context of the job-shop scheduling problem (JSP), a domain where tabu
search algorithms have been shown to be remarkably effective.
Recommendation system has been used more and more frequently in many
applications recent years. With the increasing information available, not only
in quantities but also in types, how to leverage these rich information to
build a better recommendation system becomes a natural problem. Most
traditional approaches try to design a specific model for each scenario, which
demands great efforts in developing and modifying models.
The Optiplan planning system is the first integer programming-based planner
that successfully participated in the international planning competition. This
engineering note describes the architecture of Optiplan and provides the
integer programming formulation that enabled it to perform reasonably well in
the competition. We also touch upon some recent developments that make integer
programming encodings significantly more competitive.
We study an approach to policy selection for large relational Markov Decision
Processes (MDPs). We consider a variant of approximate policy iteration (API)
that replaces the usual value-function learning step with a learning step in
policy space. This is advantageous in domains where good policies are easier to
represent and learn than the corresponding value functions, which is often the
case for the relational MDPs we are interested in. In order to apply API to
such problems, we introduce a relational policy language and corresponding
learner.
Despite recent progress in AI planning, many benchmarks remain challenging
for current planners. In many domains, the performance of a planner can greatly
be improved by discovering and exploiting information about the domain
structure that is not explicitly encoded in the initial PDDL formulation. In
this paper we present and compare two automated methods that learn relevant
information from previous experience in a domain and use it to solve new
problem instances. Our methods share a common four-step strategy.
We describe the version of the GPT planner used in the probabilistic track of
the 4th International Planning Competition (IPC-4). This version, called mGPT,
solves Markov Decision Processes specified in the PPDDL language by extracting
and using different classes of lower bounds along with various heuristic-search
algorithms. The lower bounds are extracted from deterministic relaxations where
the alternative probabilistic effects of an action are mapped into different,
independent, deterministic actions.
Logical hidden Markov models (LOHMMs) upgrade traditional hidden Markov
models to deal with sequences of structured symbols in the form of logical
atoms, rather than flat characters.
This note formally introduces LOHMMs and presents solutions to the three
central inference problems for LOHMMs: evaluation, most likely hidden state
sequence and parameter estimation. The resulting representation and algorithms
are experimentally evaluated on problems from the domain of bioinformatics.
This is the third of three papers describing ZAP, a satisfiability engine
that substantially generalizes existing tools while retaining the performance
characteristics of modern high-performance solvers. The fundamental idea
underlying ZAP is that many problems passed to such engines contain rich
internal structure that is obscured by the Boolean representation used; our
goal has been to define a representation in which this structure is apparent
and can be exploited to improve computational performance.
Partially observable Markov decision processes (POMDPs) form an attractive
and principled framework for agent planning under uncertainty. Point-based
approximate techniques for POMDPs compute a policy based on a finite set of
points collected in advance from the agents belief space. We present a
randomized point-based value iteration algorithm called Perseus. The algorithm
performs approximate value backup stages, ensuring that in each backup stage
the value of each point in the belief set is improved; the key observation is
that a single backup may improve the value of many belief points.
When dealing with incomplete data in statistical learning, or incomplete
observations in probabilistic inference, one needs to distinguish the fact that
a certain event is observed from the fact that the observed event has happened.
Since the modeling and computational complexities entailed by maintaining this
proper distinction are often prohibitive, one asks for conditions under which
it can be safely ignored. Such conditions are given by the missing at random
(mar) and coarsened at random (car) assumptions.
This paper extends the framework of partially observable Markov decision
processes (POMDPs) to multi-agent settings by incorporating the notion of agent
models into the state space. Agents maintain beliefs over physical states of
the environment and over models of other agents, and they use Bayesian updates
to maintain their beliefs over time. The solutions map belief states to
actions. Models of other agents may include their belief states and are related
to agent types considered in games of incomplete information.
Stochastic processes that involve the creation of objects and relations over
time are widespread, but relatively poorly studied. For example, accurate fault
diagnosis in factory assembly processes requires inferring the probabilities of
erroneous assembly operations, but doing this efficiently and accurately is
difficult. Modeled as dynamic Bayesian networks, these processes have discrete
variables with very large domains and extremely high dimensionality.
We present a uniform non-monotonic solution to the problems of reasoning
about action on the basis of an argumentation-theoretic approach. Our theory is
provably correct relative to a sensible minimisation policy introduced on top
of a temporal propositional logic. Sophisticated problem domains can be
formalised in our framework.
In this paper we present a new approach to modeling finite set domain
constraint problems using Reduced Ordered Binary Decision Diagrams (ROBDDs). We
show that it is possible to construct an efficient set domain propagator which
compactly represents many set domains and set constraints using ROBDDs.
We present a novel approach to the automatic acquisition of taxonomies or
concept hierarchies from a text corpus. The approach is based on Formal Concept
Analysis (FCA), a method mainly used for the analysis of data, i.e. for
investigating and processing explicitly given information. We follow Harris
distributional hypothesis and model the context of a certain term as a vector
representing syntactic dependencies which are automatically acquired from the
text corpus with a linguistic parser.
This is the second of three planned papers describing ZAP, a satisfiability
engine that substantially generalizes existing tools while retaining the
performance characteristics of modern high performance solvers. The fundamental
idea underlying ZAP is that many problems passed to such engines contain rich
internal structure that is obscured by the Boolean representation used; our
goal is to define a representation in which this structure is apparent and can
easily be exploited to improve computational performance.
Variable elimination is a general technique for constraint processing. It is
often discarded because of its high space complexity. However, it can be
extremely useful when combined with other techniques. In this paper we study
the applicability of variable elimination to the challenging problem of finding
still-lifes. We illustrate several alternatives: variable elimination as a
stand-alone algorithm, interleaved with search, and as a source of good quality
lower bounds. We show that these techniques are the best known option both
theoretically and empirically.
This paper studies the problem of learning diagnostic policies from training
examples. A diagnostic policy is a complete description of the decision-making
actions of a diagnostician (i.e., tests followed by a diagnostic decision) for
all possible combinations of test results. An optimal diagnostic policy is one
that minimizes the expected total cost, which is the sum of measurement costs
and misdiagnosis costs. In most diagnostic settings, there is a tradeoff
between these two kinds of costs. This paper formalizes diagnostic decision
making as a Markov Decision Process (MDP).
Artificial general intelligence (AGI) refers to research aimed at tackling
the full problem of artificial intelligence, that is, create truly intelligent
agents. This sets it apart from most AI research which aims at solving
relatively narrow domains, such as character recognition, motion planning, or
increasing player satisfaction in games. But how do we know when an agent is
truly intelligent?
The hidden Markov model (HMM) is a generative model that treats sequential
data under the assumption that each observation is conditioned on the state of
a discrete hidden variable that evolves in time as a Markov chain. In this
paper, we derive a novel algorithm to cluster HMMs through their probability
distributions.
Publishing private data on external servers incurs the problem of how to
avoid unwanted disclosure of confidential data. We study a problem of
confidentiality in extended disjunctive logic programs and show how it can be
solved by extended abduction. In particular, we analyze how credulous
non-monotonic reasoning affects confidentiality.
Answer set programming (ASP) is a paradigm for declarative problem solving
where problems are first formalized as rule sets, i.e., answer-set programs, in
a uniform way and then solved by computing answer sets for programs. The
satisfiability modulo theories (SMT) framework follows a similar modelling
philosophy but the syntax is based on extensions of propositional logic rather
than rules. Quite recently, a translation from answer-set programs into
difference logic was provided---enabling the use of particular SMT solvers for
the computation of answer sets.
In order to give appropriate semantics to qualitative conditionals of the
form "if A then normally B", ordinal conditional functions (OCFs) ranking the
possible worlds according to their degree of plausibility can be used. An OCF
accepting all conditionals of a knowledge base R can be characterized as the
solution of a constraint satisfaction problem. We present a high-level,
declarative approach using constraint logic programming techniques for solving
this constraint satisfaction problem.
Following a recent surge in using history-based methods for resolving
perceptual aliasing in reinforcement learning, we introduce an algorithm based
on the feature reinforcement learning framework called PhiMDP. To create a
practical algorithm we devise a stochastic search procedure for a class of
context trees based on parallel tempering and a specialized proposal
distribution. We provide the first empirical evaluation for PhiMDP.
Given a set of several inputs into a system (e.g., independent variables
characterizing stimuli) and a set of several stochastically non-independent
outputs (e.g., random variables describing different aspects of responses), how
can one determine, for each of the outputs, which of the inputs it is
influenced by? The problem has applications ranging from modeling pairwise
comparisons to reconstructing mental processing architectures to conjoint
testing.
This work reports the most relevant technical aspects in the problem of
learning the \emph{Markov network structure} from data. Such problem has become
increasingly important in machine learning, and many other application fields
of machine learning. Markov networks, together with Bayesian networks, are
probabilistic graphical models, a widely used formalism for handling
probability distributions in intelligent systems. Learning graphical models
from data have been extensively applied for the case of Bayesian networks, but
for Markov networks learning it is not tractable in practice.
Crowdsourcing websites (e.g. Yahoo! Answers, Amazon Mechanical Turk, and
etc.) emerged in recent years that allow requesters from all around the world
to post tasks and seek help from an equally global pool of workers. However,
intrinsic incentive problems reside in crowdsourcing applications as workers
and requester are selfish and aim to strategically maximize their own benefit.
In this paper, we propose to provide incentives for workers to exert effort
using a novel game-theoretic model based on repeated games.
In this paper, a methodology for the automated detection and classification
of Tuberculosis(TB) is presented. Tuberculosis is a disease caused by
mycobacterium which spreads through the air and attacks low immune bodies
easily. Our methodology is based on clustering and classification that
classifies TB into two categories, Pulmonary Tuberculosis(PTB) and retroviral
PTB(RPTB) that is those with Human Immunodeficiency Virus (HIV) infection.
Initially K-means clustering is used to group the TB data into two clusters and
assigns classes to clusters.
Commute Time Distance (CTD) is a random walk based metric on graphs. CTD has
found widespread applications in many domains including personalized search,
collaborative filtering and making search engines robust against manipulation.
Our interest is inspired by the use of CTD as a metric for anomaly detection.
It has been shown that CTD can be used to simultaneously identify both global
and local anomalies. Here we propose an accurate and efficient approximation
for computing the CTD in an incremental fashion in order to facilitate
real-time applications.
Open-text (or open-domain) semantic parsers are designed to interpret any
statement in natural language by inferring a corresponding meaning
representation (MR). Unfortunately, large scale systems cannot be easily
machine-learned due to lack of directly supervised data. We propose here a
method that learns to assign MRs to a wide range of text (using a dictionary of
more than 70,000 words, which are mapped to more than 40,000 entities) thanks
to a training scheme that combines learning from WordNet and ConceptNet with
learning from raw text.
The superiority and inferiority ranking (SIR) method is a generation of the
well-known PROMETHEE method, which can be more efficient to deal with
multi-criterion decision making (MCDM) problem. Intuitionistic fuzzy sets
(IFSs), as an important extension of fuzzy sets (IFs), include both membership
functions and non-membership functions and can be used to, more precisely
describe uncertain information. In real world, decision situations are usually
under uncertain environment and involve multiple individuals who have their own
points of view on handing of decision problems.
In recent years, there has been much interest in phase transitions of
combinatorial problems. Phase transitions have been successfully used to
analyze combinatorial optimization problems, characterize their typical-case
features and locate the hardest problem instances. In this paper, we study
phase transitions of the asymmetric Traveling Salesman Problem (ATSP), an
NP-hard combinatorial optimization problem that has many real-world
applications.
We propose a model for errors in sung queries, a variant of the hidden Markov
model (HMM). This is a solution to the problem of identifying the degree of
similarity between a (typically error-laden) sung query and a potential target
in a database of musical works, an important problem in the field of music
information retrieval. Similarity metrics are a critical component of
query-by-humming (QBH) applications which search audio and multimedia databases
for strong matches to oral queries.
Standard value function approaches to finding policies for Partially
Observable Markov Decision Processes (POMDPs) are generally considered to be
intractable for large models. The intractability of these algorithms is to a
large extent a consequence of computing an exact, optimal policy over the
entire belief space. However, in real-world POMDP problems, computing the
optimal policy for the full belief space is often unnecessary for good control
even for problems with complicated policy classes.
Decentralized control of cooperative systems captures the operation of a
group of decision makers that share a single global objective. The difficulty
in solving optimally such problems arises when the agents lack full
observability of the global state of the system when they operate. The general
problem has been shown to be NEXP-complete. In this paper, we identify classes
of decentralized control problems whose complexity ranges between NEXP and P.
In particular, we study problems characterized by independent transitions,
independent observations, and goal-oriented objective functions.
In this paper, we confront the problem of applying reinforcement learning to
agents that perceive the environment through many sensors and that can perform
parallel actions using many actuators as is the case in complex autonomous
robots. We argue that reinforcement learning can only be successfully applied
to this case if strong assumptions are made on the characteristics of the
environment in which the learning is performed, so that the relevant sensor
readings and motor commands can be readily identified.
We explore a method for computing admissible heuristic evaluation functions
for search problems. It utilizes pattern databases, which are precomputed
tables of the exact cost of solving various subproblems of an existing problem.
Unlike standard pattern database heuristics, however, we partition our problems
into disjoint subproblems, so that the costs of solving the different
subproblems can be added together without overestimating the cost of solving
the original problem.
This paper is concerned with algorithms for prediction of discrete sequences
over a finite alphabet, using variable order Markov models. The class of such
algorithms is large and in principle includes any lossless compression
algorithm. We focus on six prominent prediction algorithms, including Context
Tree Weighting (CTW), Prediction by Partial Match (PPM) and Probabilistic
Suffix Trees (PSTs). We discuss the properties of these algorithms and compare
their performance using real life sequences from three domains: proteins,
English text and music pieces.
Many known planning tasks have inherent constraints concerning the best order
in which to achieve the goals. A number of research efforts have been made to
detect such constraints and to use them for guiding search, in the hope of
speeding up the planning process. We go beyond the previous approaches by
considering ordering constraints not only over the (top-level) goals, but also
over the sub-goals that will necessarily arise during planning. Landmarks are
facts that must be true at some point in every valid solution plan.
Value iteration is a popular algorithm for finding near optimal policies for
POMDPs. It is inefficient due to the need to account for the entire belief
space, which necessitates the solution of large numbers of linear programs. In
this paper, we study value iteration restricted to belief subsets. We show
that, together with properly chosen belief subsets, restricted value iteration
yields near-optimal policies and we give a condition for determining whether a
given belief subset would bring about savings in space and time.
Many researchers in artificial intelligence are beginning to explore the use
of soft constraints to express a set of (possibly conflicting) problem
requirements. A soft constraint is a function defined on a collection of
variables which associates some measure of desirability with each possible
combination of values for those variables. However, the crucial question of the
computational complexity of finding the optimal solution to a collection of
soft constraints has so far received very little attention.
Efficient implementations of DPLL with the addition of clause learning are
the fastest complete Boolean satisfiability solvers and can handle many
significant real-world problems, such as verification, planning and design.
Despite its importance, little is known of the ultimate strengths and
limitations of the technique. This paper presents the first precise
characterization of clause learning as a proof system (CL), and begins the task
of understanding its power by relating it to the well-studied resolution proof
system.
Argumentation is based on the exchange and valuation of interacting
arguments, followed by the selection of the most acceptable of them (for
example, in order to take a decision, to make a choice).
Inductive learning is based on inferring a general rule from a finite data
set and using it to label new data. In transduction one attempts to solve the
problem of using a labeled training set to label a set of unlabeled points,
which are given to the learner prior to learning. Although transduction seems
at the outset to be an easier task than induction, there have not been many
provably useful algorithms for transduction. Moreover, the precise relation
between induction and transduction has not yet been determined.
We address the problem of finding the shortest path between two points in an
unknown real physical environment, where a traveling agent must move around in
the environment to explore unknown territory. We introduce the Physical-A*
algorithm (PHA*) for solving this problem. PHA* expands all the mandatory nodes
that A* would expand and returns the shortest path between the two points.
However, due to the physical nature of the problem, the complexity of the
algorithm is measured by the traveling effort of the moving agent and not by
the number of generated nodes, as in standard A*.
This is the first of three planned papers describing ZAP, a satisfiability
engine that substantially generalizes existing tools while retaining the
performance characteristics of modern high-performance solvers. The fundamental
idea underlying ZAP is that many problems passed to such engines contain rich
internal structure that is obscured by the Boolean representation used; our
goal is to define a representation in which this structure is apparent and can
easily be exploited to improve computational performance.
When writing a constraint program, we have to choose which variables should
be the decision variables, and how to represent the constraints on these
variables. In many cases, there is considerable choice for the decision
variables. Consider, for example, permutation problems in which we have as many
values as variables, and each variable takes an unique value. In such problems,
we can choose between a primal and a dual viewpoint. In the dual viewpoint,
each dual variable represents one of the primal values, whilst each dual value
represents one of the primal variables.
Two major goals in machine learning are the discovery and improvement of
solutions to complex problems. In this paper, we argue that complexification,
i.e. the incremental elaboration of solutions through adding new structure,
achieves both these goals. We demonstrate the power of complexification through
the NeuroEvolution of Augmenting Topologies (NEAT) method, which evolves
increasingly complex neural network architectures. NEAT is applied to an
open-ended coevolutionary robot duel domain where robot controllers compete
head to head.
A novel algorithm for actively trading stocks is presented. While traditional
expert advice and "universal" algorithms (as well as standard technical trading
heuristics) attempt to predict winners or trends, our approach relies on
predictable statistical relations between all pairs of stocks in the market.
Our empirical results on historical markets provide strong evidence that this
type of technical trading can "beat the market" and moreover, can beat the best
stock in the market. In doing so we utilize a new idea for smoothing critical
parameters in the context of expert learning.
The 2002 Trading Agent Competition (TAC) presented a challenging market game
in the domain of travel shopping. One of the pivotal issues in this domain is
uncertainty about hotel prices, which have a significant influence on the
relative cost of alternative trip schedules. Thus, virtually all participants
employ some method for predicting hotel prices. We survey approaches employed
in the tournament, finding that agents apply an interesting diversity of
techniques, taking into account differing sources of evidence bearing on
prices.
The predominant knowledge-based approach to automated model construction,
compositional modelling, employs a set of models of particular functional
components. Its inference mechanism takes a scenario describing the constituent
interacting components of a system and translates it into a useful mathematical
model. This paper presents a novel compositional modelling approach aimed at
building model repositories. It furthers the field in two respects.
We present a visually-grounded language understanding model based on a study
of how people verbally describe objects in scenes. The emphasis of the model is
on the combination of individual word meanings to produce meanings for complex
referring expressions. The model has been implemented, and it is able to
understand a broad range of spatial referring expressions. We describe our
implementation of word level visually-grounded semantics and their embedding in
a compositional parsing framework.
We introduce an abductive method for a coherent integration of independent
data-sources. The idea is to compute a list of data-facts that should be
inserted to the amalgamated database or retracted from it in order to restore
its consistency. This method is implemented by an abductive solver, called
Asystem, that applies SLDNFA-resolution on a meta-theory that relates
different, possibly contradicting, input databases.
Hierarchical latent class (HLC) models are tree-structured Bayesian networks
where leaf nodes are observed while internal nodes are latent. There are no
theoretically well justified model selection criteria for HLC models in
particular and Bayesian networks with latent nodes in general. Nonetheless,
empirical studies suggest that the BIC score is a reasonable criterion to use
in practice for learning HLC models.
We propose a formalism for representation of finite languages, referred to as
the class of IDL-expressions, which combines concepts that were only considered
in isolation in existing formalisms. The suggested applications are in natural
language processing, more specifically in surface natural language generation
and in machine translation, where a sentence is obtained by first generating a
large set of candidate sentences, represented in a compact way, and then by
filtering such a set through a parser.
The Model Checking Integrated Planning System (MIPS) is a temporal least
commitment heuristic search planner based on a flexible object-oriented
workbench architecture. Its design clearly separates explicit and symbolic
directed exploration algorithms from the set of on-line and off-line computed
estimates and associated data structures. MIPS has shown distinguished
performance in the last two international planning competitions.
Supply chain formation is the process of determining the structure and terms
of exchange relationships to enable a multilevel, multiagent production
activity. We present a simple model of supply chains, highlighting two
characteristic features: hierarchical subtask decomposition, and resource
contention. To decentralize the formation process, we introduce a market price
system over the resources produced along the chain. In a competitive
equilibrium for this system, agents choose locally optimal allocations with
respect to prices, and outcomes are optimal overall.
Information about user preferences plays a key role in automated decision
making. In many domains it is desirable to assess such preferences in a
qualitative rather than quantitative way. In this paper, we propose a
qualitative graphical representation of preferences that reflects conditional
dependence and independence of preference statements under a ceteris paribus
(all else being equal) interpretation. Such a representation is often compact
and arguably quite natural in many circumstances.
MAP is the problem of finding a most probable instantiation of a set of
variables given evidence. MAP has always been perceived to be significantly
harder than the related problems of computing the probability of a variable
instantiation Pr, or the problem of computing the most probable explanation
(MPE). This paper investigates the complexity of MAP in Bayesian networks.
Specifically, we show that MAP is complete for NP^PP and provide further
negative complexity results for algorithms based on variable elimination. We
also show that MAP remains hard even when MPE and Pr become easy.
The size and complexity of software and hardware systems have significantly
increased in the past years. As a result, it is harder to guarantee their
correct behavior. One of the most successful methods for automated verification
of finite-state systems is model checking. Most of the current model-checking
systems use binary decision diagrams (BDDs) for the representation of the
tested model and in the verification process of its properties. Generally, BDDs
allow a canonical compact representation of a boolean function (given an order
of its variables).
Although many algorithms have been designed to construct Bayesian network
structures using different approaches and principles, they all employ only two
methods: those based on independence criteria, and those based on a scoring
function and a search procedure (although some methods combine the two). Within
the score+search paradigm, the dominant approach uses local search methods in
the space of directed acyclic graphs (DAGs), where the usual choices for
defining the elementary modifications (local changes) that can be applied are
arc addition, arc deletion, and arc reversal.
This paper presents a new classifier combination technique based on the
Dempster-Shafer theory of evidence. The Dempster-Shafer theory of evidence is a
powerful method for combining measures of evidence from different classifiers.
However, since each of the available methods that estimates the evidence of
classifiers has its own limitations, we propose here a new implementation which
adapts to training data so that the overall mean square error is minimized.
Independence -- the study of what is relevant to a given problem of reasoning
-- has received an increasing attention from the AI community. In this paper,
we consider two basic forms of independence, namely, a syntactic one and a
semantic one. We show features and drawbacks of them. In particular, while the
syntactic form of independence is computationally easy to check, there are
cases in which things that intuitively are not relevant are not recognized as
such.
This paper presents an approach to expert-guided subgroup discovery. The main
step of the subgroup discovery process, the induction of subgroup descriptions,
is performed by a heuristic beam search algorithm, using a novel parametrized
definition of rule quality which is analyzed in detail.
Adjustable autonomy refers to entities dynamically varying their own
autonomy, transferring decision-making control to other entities (typically
agents transferring control to human users) in key situations. Determining
whether and when such transfers-of-control should occur is arguably the
fundamental research problem in adjustable autonomy. Previous work has
investigated various approaches to addressing this problem but has often
focused on individual agent-human interactions.
In this paper, we analyze the decision version of the NK landscape model from
the perspective of threshold phenomena and phase transitions under two random
distributions, the uniform probability model and the fixed ratio model. For the
uniform probability model, we prove that the phase transition is easy in the
sense that there is a polynomial algorithm that can solve a random instance of
the problem with the probability asymptotic to 1 as the problem size tends to
infinity.
We develop, analyze, and evaluate a novel, supervised, specific-to-general
learner for a simple temporal logic and use the resulting algorithm to learn
visual event definitions from video sequences. First, we introduce a simple,
propositional, temporal, event-description language called AMA that is
sufficiently expressive to represent many events yet sufficiently restrictive
to support learning. We then give algorithms, along with lower and upper
complexity bounds, for the subsumption and generalization problems for AMA
formulas.
Despite the significant progress in multiagent teamwork, existing research
does not address the optimality of its prescriptions nor the complexity of the
teamwork problem. Without a characterization of the optimality-complexity
tradeoffs, it is impossible to determine whether the assumptions and
approximations made by a particular theory gain enough efficiency to justify
the losses in overall performance. To provide a tool for use by multiagent
researchers in evaluating this tradeoff, we present a unified framework, the
COMmunicative Multiagent Team Decision Problem (COM-MTDP).
In recent years research in the planning community has moved increasingly
toward s application of planners to realistic problems involving both time and
many typ es of resources. For example, interest in planning demonstrated by the
space res earch community has inspired work in observation scheduling,
planetary rover ex ploration and spacecraft control domains.
For large, real-world inductive learning problems, the number of training
examples often must be limited due to the costs associated with procuring,
preparing, and storing the training examples and/or the computational costs
associated with learning from them. In such circumstances, one question of
practical importance is: if only n training examples can be selected, in what
proportion should the classes be represented?
Prediction markets show considerable promise for developing flexible
mechanisms for machine learning. Here, machine learning markets for
multivariate systems are defined, and a utility-based framework is established
for their analysis. This differs from the usual approach of defining static
betting functions. It is shown that such markets can implement model
combination methods used in machine learning, such as product of expert and
mixture of expert approaches as equilibrium pricing models, by varying agent
utility functions.
In this paper we explore a symmetry-based search space reduction technique
which can speed up optimal pathfinding on undirected uniform-cost grid maps by
up to 38 times. Our technique decomposes grid maps into a set of empty
rectangles, removing from each rectangle all interior nodes and possibly some
from along the perimeter. We then add a series of macro-edges between selected
pairs of remaining perimeter nodes to facilitate provably optimal traversal
through each rectangle. We also develop a novel online pruning technique to
further speed up search.
This preliminary report addresses the expressive power of unit resolution
regarding input data encoded with partial truth assignments of propositional
variables. A characterization of the functions that are computable in this way,
which we propose to call propagatable functions, is given. By establishing that
propagatable functions can also be computed using monotone circuits, we show
that there exist polynomial time complexity propagable functions requiring an
exponential amount of clauses to be computed using unit resolution.
In the current study we examine an application of the machine learning
methods to model the retention constants in the thin layer chromatography
(TLC). This problem can be described with hundreds or even thousands of
descriptors relevant to various molecular properties, most of them redundant
and not relevant for the retention constant prediction. Hence we employed
feature selection to significantly reduce the number of attributes.
Additionally we have tested application of the bagging procedure to the feature
selection.