Florin Constantin


florin@cc.gatech.edu

I am a postdoctoral fellow in the College of Computing at the Georgia Institute of Technology.
I work under the supervision of Prof. Nina Balcan and Prof. Jeff Shamma.

My research interests (see my research statement) touch on game theory (in particular mechanism design), algorithms and artificial intelligence.

Until June 2009, I was a Ph.D. candidate in the EconCS Group in the School of Engineering and Applied Sciences at Harvard University.
My advisor was Prof. David C. Parkes.

I am on the Program Committee of the 11th ACM Conference on Electronic Commerce, to be held June 7-11, 2010 at Harvard University.

Publications

Self-Correcting Sampling-Based Dynamic Multi-Unit Auctions

by Florin Constantin and David C. Parkes.

In the Proceedings of the ACM Conference on Electronic Commerce (EC) 2009.

We present the first use of online stochastic optimization for incentive-compatible dynamic auctions with partially patient, multi-unit demand bidders.
We achieve strategyproofness via a self-correcting procedure applied to a heuristic version of the Consensus algorithm.
We show empirically that the price of strategyproofness is limited with respect to both performance and computation requirements.

Explanatory slides.




Online Ad Slotting With Cancellations

by Florin Constantin, Jon Feldman, S. Muthukrishnan and Martin Pál.

In the Fourth Workshop on Ad Auctions, Chicago 2008.

An updated version:

An Online Mechanism for Ad Slot Reservations with Cancellations

by Florin Constantin, Jon Feldman, S. Muthukrishnan and Martin Pál.

In the Proceedings of the Symposium on Discrete Algorithms (SODA) 2009.

Many display advertisements (ads) are sold via spot auctions. A currently missing, desirable, feature is the reservation of ad slots in advance. We introduce a simple model for auctioning ad slot reservations, in which impatient private-value unit-demand bidders arrive sequentially. The seller can cancel at any time an earlier reservation, resulting in a utility loss to the reservation holder of a fraction of her value.

Our main result is an online mechanism with many desirable game-theoretic and optimization properties. Winners have an incentive to be honest and bidding one's true value dominates any lower bid. Our mechanism's revenue is within a constant fraction of the a posteriori revenue of the Vickrey-Clarke-Groves mechanism. Our mechanism's efficiency is within a constant fraction of the a posteriori optimally efficient solution. If efficiency also takes into account the utility losses of bidders whose reservation was canceled, our mechanism can match an upper bound on the competitive ratio of any deterministic online algorithm.


Extension to multi-unit demand

Online multi-unit auctions with costly cancellations

by Florin Constantin and David C. Parkes.

Under preparation.

We extend the semi-online unit-demand reservations with costly cancellations model to multi-unit demand bidders with decreasing marginal values.
We show how a natural extension of the unit-demand pricing scheme loses important incentive properties.
We recover the property that bidding true value(s) dominates any lower bid together with (slightly weaker) optimization properties by a simple modification in the pricing scheme.

My Ad Auction Workshop slides

Online Auctions for Bidders with Interdependent Values

by Florin Constantin, Takayuki Ito and David C. Parkes.


In the Proceedings of the International Conference on Autonomous Agents and Multiagent Systems (AAMAS), 2007 (poster paper).

Interdependent values (IDV) is a valuation model allowing bidders in an auction to express their value for the item(s) to sell as a function of the other bidders' information. We investigate the incentive compatibility (IC) of single-item auctions for IDV bidders in dynamic environments. We provide a necessary and sufficient characterization for IC in this seting. We show that if bidders can misreport departure times and private signals, no reasonable auction can be IC. We present a reasonable IC auction for the case where bidders cannot misreport departures.


On Revenue-Optimal Dynamic Auctions for Bidders with Interdependent Values

by Florin Constantin and David C. Parkes.


In the Proceedings of the Ninth Workshop on Agent Mediated Electronic Commerce, 2007.

We adopt a computational approach to design single-item revenue-optimal dynamic auctions with known arrivals and departures but (private) signals that arrive online.
In leveraging a characterization of truthful auctions, we present a mixed-integer programming formulation of the design problem.
We highlight general properties of revenue-optimal dynamic auctions in a simple parameterized example and study the sensitivity of prices and revenue to model parameters.

More on the Power of Demand Queries in Combinatorial Auctions: Learning Atomic Languages and Handling Incentives

by Sébastien Lahaie, Florin Constantin and David C. Parkes.

In the Proceedings of the 19th International Joint Conference on Artificial Intelligence, 2005.

We define a learning algorithm for atomic bidding languages, a class of languages that includes both OR and XOR.
We characterize the communication requirements of the Vickrey-Clarke-Groves outcome rule and show how to bring truthful responses to demand queries in an equilibrium.

Preference-Based Characterizations of Truthfulness and the Limited Expressiveness of Order-Based Domains

by Florin Constantin and David C. Parkes.


In the Proceedings of the Workshop on Preference Handling, Edinburgh, Scotland, August 2005 (Position Paper).

We highlight the limited applicability of existing characterizations of truthfulness when applied to relevant domains.
We suggest relevant domain classes that are modular extensions to ones for which characterizations of truthfulness exist.
We also advocate the use of natural (critical-value-based) payment schemes.

Slides

Tracking a moving object with a binary sensor network

by Javed Aslam, Zack Butler, Florin Constantin, Valentino Crespi, George Cybenko and Daniela Rus (my advisor at Dartmouth College).

In the Proceedings of ACM SenSys'03.

We propose a binary sensor model where each sensor can only detect whether a tracked object is moving towards or away from it.
We highlight geometric properties induced by this model and incorporate them in a particle-filtering tracking algorithm.
We present an analysis of a fundamental limitation of this model and show how it can be overcome with the addition of a proximity bit for each sensor.

Teaching

Coursework

Personal

I enjoy playing bridge (meet my very patient partner and cousin Virgil Pavlu) and soccer. Feel free to contact me if you want to learn bridge or to teach me how to play soccer.