Research Interests
Intelligent Virtual Agents, Reasoning About Navigation, Hybrid Systems,
Game Artificial Intelligence, Behavioral Animation/Robotics, Applied
Logic, Cognitive Modeling, Automated Reasoning and Verification,
Eyetracking and Attention, Simplicial and Multigrid Methods, Tumor Modeling
CV/List of Publications
My CV is available in PDF and PS
formats.
There is a text/html list of my publications,
some of which are briefly described in other sections of my web pages.
A few recent papers:
- Hybrid System Models of Navigation Strategies for Games and Animations.
E. Aaron, F. Ivancic, and D. Metaxas.
Proceedings of Hybrid Systems: Computation and Control, LNCS 2289,
7-20, 2002.
- Scalable Nonlinear Dynamical Systems for Agent Steering and Crowd Simulation.
S. Goldenstein, M. Karavelas, D. Metaxas, L. Guibas, E. Aaron, and A. Goswami.
Computers And Graphics, 25(6), 983-998, 2001.
- A Framework for Reasoning about Animation Systems.
E. Aaron, D. Metaxas, F. Ivancic, and O. Sokolsky.
Proceedings of the Third International Workshop on Intelligent
Virtual Agents, LNAI 2190, 47-60, 2001.
Primary Research Focus: Verifiable Dynamic Actors
Motivated by animation, video game development, and robotics, we are
developing models of autonomous intelligent actors
(e.g., animated agents, navigating robots) that jointly satisfy
three goals:
- Models capture the low-level evolution of an actor's
physical and cognitive states as it moves through its
world.
- Models can be designed in keeping with natural
abstractions that designers wish to apply.
- Models support automated assistance in verifying dynamic
properties of these actors in dynamic worlds (e.g., with moving
targets/goals and moving obstacles).
Our modeling approach is based upon the theoretical framework
of hybrid dynamical systems (hybrid systems,
for short), i.e., systems that combine continuous and discrete
dynamics. Hybrid system-based models allow access to low-level
dynamics within a state-transition framework. Spatio-temporal
properties of the models may be formalized in expressive modal
logic formulas for which there are established procedures for
verification (model checking).
We began by making a concrete connection between hybrid system theory and
animation: We directly applied the general-purpose hybrid system modeling tool
CHARON to generate
multi-agent animations with respect to well-understood theoretical system models.
This was a novel, systems-level understanding of navigation strategy for autonomous
actors
and a proof of concept that the two disparate disciplines could be productively
related.
Motivated by the hybrid systems framework, we also designed and implemented
a novel high-level navigation system in CHARON. In particular, our system guides
the high-level behavior of actors moving through a virtual city. (We contrast
global, high-level behavior with local, low-level behavior. For instance, avoiding
immediate obstacles and other tasks on the order of local perception are low-level;
street selection is high-level.)
Each actor has its own mental map and subjective perception of attributes of
the world around it. Each actor makes its own navigation decisions in real time,
based on the dynamically changing values of attributes in the world around it
and
its dynamically changing priorities. We coupled this high-level navigation system
with the low-level system described above, creating a single hierarchical hybrid
system for navigating intelligent virtual agents.
We are also exploring ways to apply tools and methods for verifying hybrid systems
to verify animation systems. In particular, having employed approximation
and abstraction techniques to avoid decidability restrictions on our
complex dynamical systems, we have created a verifier (in MATLAB) that performs
model-checking on reachability properties of our hybrid system models. With
it, we can answer questions about areas such as:
- Quantifiable relative difficulty of
different worlds (with multiple metrics);
- Collision-avoidance of dynamic wayfinding actors;
- Cinematographic constraints for animation.
Our primary focus is on animations, but our work also has natural applications to robotics.
Animations/Demos
(Please note: Links in this section may refer to my Web pages at Rutgers
University.)
As part of our research, we generated some multi-agent
animations using MATLAB or the hybrid system specification and simulation
tool CHARON.
For the most part, these animations are cited in our publications, such as:
- Supplementary material
for A Hybrid Dynamical Systems Approach to Intelligent Low-Level Navigation.
E. Aaron, H. Sun, F. Ivancic, and D. Metaxas.
Proceedings of Computer Animation 2002, 154-163, 2002.
- Supplementary
material for Hybrid System Models of Navigation Strategies for Games
and Animations.
E. Aaron, F. Ivancic, and D. Metaxas.
Proceedings of Hybrid Systems: Computation and Control, LNCS 2289, 7-20, 2002.
- Supplementary
material for A Framework for Reasoning about Animation Systems.
E. Aaron, D. Metaxas, F. Ivancic, and O. Sokolsky.
Proceedings of the Third International Workshop on Intelligent
Virtual Agents, LNAI 2190, 47-60, 2001.
Supplementary materials for papers often include CHARON output and other information as well as animations.
Other Research Areas and Interests
Cognitive Logical Inference and Student Modeling
Before turning my attention
to intelligent virtual agents and animation systems, I
developed formalized mathematical tactics for cognitive
inference modeling.
Like the Verifiable Dynamic Actors work, this is also
Verification-Motivated Intelligence Modeling; this area, too,
involves developing models of complex intelligent behavior in a
framework that supports fine-grained, detailed analysis. Unlike
the hybrid systems and model checking frameworks for Verifiable
Dynamic Actors, however, these models utilize the highly
rigorous methods of tactic-based automated theorem proving.
I concentrated in particular on developing a model of undergraduate students
carrying out logical proofs in a structured framework, but the ideas underlying
the work are not student-specific. The many facets of this work are described
in my dissertation, Tactic-Based Modeling of Cognitive Inference on Logically
Structured Notation. I have also written papers on its components, which
range from logic and formalized mathematics (Justifying calculational
logic by a conventional metalinguistic semantics) to cognitive science
and eyetracking research (Insight into theorem proving via eye movements).
To conserve space here, I put a brief but significantly
more descriptive introduction to my dissertation research on a separate
page.
Explanation
Related to all the research areas noted above, I am also
interested in the phenomenon of explanation,
effectively expressing and evaluating the results of analysis.
Explanation has a particularly interesting connection to
verification: The full depth and detail of verification may not
be necessary for explaining the results of analysis to every
possible audience, but a verification-oriented analysis
provides a rich foundation for a range of possible
explanations.
Explanation is a high-level goal, built on top of the models of intelligence.
The Verifiable Dynamic Actors project is not yet able to support explanation-oriented
results, although that is an eventual goal. In the Student Modeling work, there
is a persistent concern with explanation: We build up from simple axioms and
rules to complex tactics that capture how students explain their inference (in
accord with externally specified, normative standards).
In addition, my paper Frequency vs. probability formats: Framing the
three doors problem (more description) touches upon the topic in an experimental
psychology context. It investigates how well people understand how they arrive
at their answer when confronted with "The Monty Hall Problem."
Other Noteworthy Publications
- Modal Logic Semantics
One way to avoid difficulties with partial functions is by
employing the notion of underspecification. In modal
logic S5 and some semantically related logics,
underspecification preserves validity, so incorporating
underspecification into their semantics does not change the
classes of valid formulae. A formalization of
underspecification and results for these modal logics are
concisely presented in Formal justification of
underspecification for S5. (co-author: David Gries)
- The Three Doors Problem
The notorious brainteaser "The Three Doors Problem" (also called "The Monty Hall
Problem") is the source of much debate. Would people be more likely
to correctly perform the underlying mathematics if the puzzle were presented
in a frequency format rather than a probability format?
Would people be more likely to arrive at the correct answer?
Results are reported in Frequency vs. probability
formats: Framing the three doors problem
(PDF version). (co-author: Michael Spivey)
- Nuprl
Most documentation about the Nuprl automated reasoning system
has been written from an "insider's"
perspective. I used the system but was not involved in its
development; I have a user's perspective. My A
User-Level Introduction to the Nuprl Proof Development System
(PS version) was solicited by the Nuprl
group at Cornell University.
Non-academic stuff
Music is one of my most important non-academic interests. I
have written about music (album reviews
and features), broadcast as a jazz DJ (a weekly
commercial radio show), and played in a few rock bands
that successfully made it out of the garage.
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