Hi.
I joined the Department of
Combinatorics and Optimization at the University of
Waterloo as an assistant professor in September 2006.
Previously I was a postdoctoral scholar at the
Center for the Mathematics of Information (CMI)
at Caltech.
I graduated from the Department of Computer Science
at Cornell University in May 2004.
My advisor was David Shmoys.
For research, I mostly think about algorithms. My research interests include
combinatorial optimization, approximation algorithms, algorithmic game theory,
stochastic optimization, network design, scheduling, and online algorithms.
Combinatorial Algorithms for Rooted PrizeCollecting
Walks and their Applications to Orienteering
(with Ian Post).

ConstantFactor Approximation to Deadline TSP and
Related Problems in (Almost) Quasipolynomial Time
(with Zachary Friggstad).

Approximation Algorithms for Stochastic Minimum Norm
Combinatorial Optimization
(with Sharat Ibrahimpur).

Sampling Bounds and Algorithms for Distributionally Robust
Stochastic Optimization with Arbitrary BlackBox Distributions
(with Andre Linhares).

A ConstantFactor Approximation for Directed Latency in
Quasipolynomial Time
(with Zachary Friggstad). ESA 2020. 
Simpler and Better Algorithms for MinimumNorm Load Balancing
(with Deeparnab Chakrabarty). ESA 2019. 
Approximation Algorithms for Distributionally Robust
Stochastic Optimization with BlackBox Distributions
(with Andre Linhares). STOC 2019. 
Approximation Algorithms for Minimum Norm and Ordered
Optimization Problems
(with Deeparnab Chakrabarty). STOC 2019. 
Approximate MultiMatroid Intersection via Iterative
Refinement
(with Andre Linhares, Neil Olver, and
Rico Zenklusen). IPCO 2019. 
Algorithms for Inverse Optimization Problems
(with Sara Ahmadian,
Umang Bhaskar, and
Laura Sanita). ESA 2018. 
Minimizing Latency in Online Ride and Delivery Services (with
Abhimanyu Das,
Sreenivas Gollapudi,
Anthony Kim, and
Debmalya Penigrahi). WWW 2018. Received the honorable mention research paper citation. 
Interpolating
between kMedian and kCenter: Approximation Algorithms for
Ordered kMedian (with
Deeparnab Chakrabarty). Proceedings of ICALP 2018, pages 29:129:14. Detailed version posted on the CS arXiv, November 2017. Detailed vresion ps, pdf or conference version pdf. 
On the Integrality Gap of the
PrizeCollecting Steiner Forest LP (with
Jochen Koenemann,
Neil Olver,
Kanstantsin Pashkovich,
R. Ravi, and
Jens Vygen). Proceedings of APPROX 2017, pages 17:117:13. Detailed version posted on the CS arXiv, June 2017. Detailed version pdf or conference version pdf. 
Orienteering Algorithms for
Generating Travel Itineraries (with
Zachary Friggstad,
Sreenivas Gollapudi,
Kostas Kollias,
Tamas Sarlos, and
Andrew Tomkins). To appear in Proceedings of the ACM International Conference on Web Search and Data Mining (WSDM) 2018. pdf. 
Improved Algorithms for MST and
MetricTSP Interdiction (with Andre Linhares). Proceedings of ICALP 2017, pages 32:132:14. Detailed version posted on the CS arXiv, June 2017. Detailed version ps, pdf or conference version pdf. Slides: Short version (ppt). Presented at Banff Workshop on Approximation Algorithms and Hardness of Approximation, November 2017 (video). 
Compact, ProvablyGood LPs
for Orienteering and RegretBounded Vehicle Routing
(with Zachary Friggstad). Proceedings of IPCO 2017, pages 199211. Detailed version posted on the CS arXiv, August 2017. Detailed version pdf or conference version pdf. Slides: Short version (ppt). Presented at Algorithms and Uncertainty Seminar, Simons Institute, UC Berkeley, December 2016; IPCO, July 2017; Simons Workshop on "Discrete Optimization via Continuous Relaxation", September 2017 (video); 
MinMax Theorems for Packing and
Covering Odd (u, v)Trails (with Sharat Ibrahimpur). Proceedings of IPCO 2017, pages 279291. Detailed version posted on the CS arXiv, August 2017. Detailed version pdf or conference version pdf. 
Hardness Results for Signaling
in Bayesian ZeroSum and Network Routing Games (with
Umang Bhaskar,
Yu Cheng and
Young Kun Ko). Proceedings of EC 2016, pages 479496. ps or pdf. Slides: Short version (ppt). Presented at Tutte seminar at the University of Waterloo, January 2016; HIM Game Theory Workshop, Bonn, December 2016 (video). 
Approximation Algorithms for
Clustering Problems with Lower Bounds and Outliers
(with Sara Ahmadian). Proceedings of ICALP 2016, pages 69:169:15. Detailed version posted on the CS arXiv, August 2016. Detailed version pdf or conference version pdf. 
Approximating MinCost
ChainConstrained Spanning Trees: A Reduction from Weighted to Unweighted
Problems (with Andre Linhares). Mathematical Programming, 172(12):1734, 2018. Preliminary version in Proceedings of IPCO 2016, pages 3849. Journal version ps, pdf or conference version ps, pdf. Slides: Long version (ppt). Presented at 6th Cargese Workshop on Combinatorial Optimization, September 2015; INFORMS Annual Meeting (invited talk), November 2016; CMS Winter Meeting (invited talk), December 2016. 
Learning Arbitrary Statistical
Mixtures of Discrete Distributions (with
Jian Li,
Yuval Rabani
and Leonard Schulman). Proceedings of STOC 2015, pages 743752. Detailed version posted on the CS arXiv, Apr 2015. Detailed version ps, pdf or conference version ps, pdf. 
LinearProgramming based
Approximation Algorithms for MultiVehicle Minimum Latency Problems
(with Ian Post). Proceedings of SODA 2015, pages 512531. Detailed version posted on the CS arXiv, November 2014. Detailed version ps, pdf or conference version ps, pdf. Slides: Long version (ppt) or short version (ppt). Presented at 7th Workshop on Flexible Network Design, Lugano, August 2014; Tutte seminar at the University of Waterloo, October 2014; SODA, January 2015. 
Improved RegionGrowing and
Combinatorial Algorithms for kRoute Cut Problems (with Guru
Guruganesh and Laura Sanita). Proceedings of SODA 2015, pages 676695. Also posted on the CS arXiv, October 2014. ArXiv version pdf, or conference version pdf. Slides: Short version (ppt). Presented at Banff Workshop on Approximation Algorithms and Hardness of Approximation, August 2014 (video); Bridging Discrete and Continuous Optimization Seminar, Simons Institute, UC Berkeley, October 2017. 
Achieving Target Equilibria in
Network Routing Games without Knowing the Latency Functions
(with Umang Bhaskar,
Katrina Ligett,
and Leonard Schulman). Invited to a special issue of Games and Economic Behavior devoted to selected papers from SODA, FOCS, STOC 2014. Preliminary version in Proceedings of FOCS 2014, pages 3140. Detailed version pdf or conference version ps, pdf. 
Approximation
Algorithms for MinimumLoad kFacility Location
(with Sara
Ahmadian, Babak
Behsaz, Zachary Friggstad,
Amin Jorati,
and Mohammad Salavatipour). Transactions on Algorithms, 14(2):article 16, 2018. Preliminary version in Proceedings of APPROX 2014, pages 1733. Journal version pdf or conference version pdf. 
Improved Approximation
Algorithms for Matroid and Knapsack Median Problems and Applications. ACM Transactions on Algorithms, 12(4), article no. 49, 2016. Preliminary version in Proceedings of APPROX 2014, pages 403418. Journal version ps, pdf, or conference version pdf. Slides: Short version (ppt). Presented at APPROX, August 2014. 
Approximation Algorithms for
RegretBounded Vehicle Routing and Applications to DistanceConstrained Vehicle
Routing (with Zachary
Friggstad). Proceedings of STOC 2014, pages 744753. Detailed version posted on the CS arXiv, November 2013. Detailed version pdf or conference version ps or pdf. Slides: Long version (ppt) or a (slightly) shorter version (ppt). Presented at STOC, June 2014; ISMP (invited talk), July 2015; Google, Mountain View, December 2016. 
Welfare Maximization and
Truthfulness in Mechanism Design with Ordinal Preferences
(with Deeparnab
Chakrabarty). Proceedings of ITCS 2014, pages 105120. Also posted on the CS arXiv, December 2013. ArXiv version ps, pdf, or conference version ps, pdf. Slides: Long version (ppt) or short version (ppt). Presented at CORSINFORMS International Meeting (invited talk), May 2014; Bellairs Workshop on Algorithmic Game Theory, April 2014; ITCS, January 2014. 
Learning Mixtures of
Arbitrary Distributions over Large Discrete Domains
(with Yuval Rabani
and Leonard Schulman). Proceedings of ITCS 2014, pages 207224. Also posted on the CS arXiv, September 2012. ArXiv version ps, pdf, or conference version ps, pdf. Slides: Short version (ppt). Presented at ITCS, January 2014. 
NearOptimal and Robust
Mechanism Design for Covering Problems with Correlated Players (with Hadi
Minooei). ACM Transactions on Economics and Computation, 3(4), article no. 19, 2015. Special issue devoted to selected papers from WINE 2013. Preliminary version in Proceedings of WINE 2013, pages 377390. Journal version ps or pdf. Note: The journal version has some significant differences with the conference version. It better elucidates the differences between covering and packing mechanism design, and corrects a few errors in the conference version; you are therefore encouraged to consult the journal version. The key differences between the conference and journal versions are: (a) The IC and IR notion we propose are denoted supportbased (IC, IR) in the journal version instead of robust(BIC, IR). (b) Additive types are defined more accurately in the journal version; these correspond to additive valuations for combinatorial auctions. (c) Approximation algorithms for the SWM problem are leveraged for revenuemaximization only for singledimensional domains. (This proceeds in a simple and standard way and does not run into any of the difficulties encountered for covering problems.) 
LocalSearch based
Approximation Algorithms for Mobile Facility Location Problems (with
Sara Ahmadian
and Zachary Friggstad). Proceedings of SODA 2013, pages 16071621. Detailed version posted on the CS arXiv, January 2013. Detailed version ps, pdf or conference version ps, pdf. Note: A subtle error in the definition of cand(i) and some typos in the conference publication have been corrected in the versions posted above. 
Truthful Mechanism Design
for Multidimensional Covering Problems (with Hadi Minooei). Proceedings of WINE 2012, pages 448461. Detailed version posted on the CS arXiv, November 2012. Detailed version pdf or conference version ps, pdf. Note: Theorem 13 in the conference publication is incorrect. The claimed guarantee holds if we assume that any two nodes owned by the same player are at least hopdistance 3 away from each other. The correct guarantee in general is: O(γ r log n)approximation for an everywhere γsparse graph, which leads to an O(r log n)approximation for any proper minorclosed family of graphs. This has been corrected in the versions posted above (and on the arXiv). The corrected statement appears as Theorem 4.10 in the detailed version, and Theorem 15 in the conference version. 
BlackBox
Reductions for CostSharing Mechanism Design
(with Konstantinos Georgiou). To appear in Games and Economic Behavior. Special issue devoted selected papers from SODA, FOCS, STOC 2012. Preliminary version in Proceedings of SODA 2012, pages 896913. Journal version ps, pdf or conference version ps, pdf. Slides: Long version (ppt). Presented at SODA, January 2012; Bellairs Workshop on Algorithmic Game Theory, April 2012; Dept. of Computing and Software Seminar at McMaster University, September 2012; IST Lunch Bunch Seminar, Caltech, October 2012. 
Improved Approximation Guarantees for LowerBounded
Facility Location
(with Sara Ahmadian). Proceedings of WAOA 2012, pages 257271. Detailed version posted on the CS arXiv, August 2012. Detailed version ps, pdf or conference version ps, pdf. 
RiskAverse Stochastic Optimization:
ProbabilisticallyConstrained Models and Algorithms for BlackBox Distributions. Proceedings of SODA 2011, pages 16271646. ps or pdf. An older version appeared as "Algorithms for ProbabilisticallyConstrained Models of RiskAverse Stochastic Optimization with BlackBox Distributions" on the CS arXiv; a newer detailed version will be posted soon. Slides: Long version (ppt) or a (slightly) shorter version (ppt). Presented at 3rd Workshop on Flexible Network Design, July 2008; Theory seminar at Cornell University, September 2008; Dagstuhl Workshop on Algorithm Engineering, June 2010; SODA, January 2011; ISMP (invited talk), August 2012. 
Facility Location with Client
Latencies: LinearProgramming based Techniques for MinimumLatency Problems
(with Deeparnab Chakrabarty). Mathematics of Operations Research, 41(3):865883, 2016. Preliminary version in Proceedings of IPCO 2011, pages 92103. Journal version ps, pdf or conference version ps, pdf. Slides: Long version (ppt) or short version (ppt). Presented at IPCO, June 2011; Tutte seminar at the University of Waterloo, July 2011; Banff Workshop on Approximation Algorithms and Hardness of Approximation, November 2011; 5th Workshop on Flexible Network Design, Warsaw, July 2012; Theory seminar at RWTH Aachen University, August 2012. 
FaultTolerant Facility Location: A
Randomized Dependent LProunding Algorithm
(with Jaroslaw Byrka
and Aravind Srinivasan). Proceedings of IPCO 2010, pages 244257. Detailed version ps, pdf or conference version ps, pdf. 
Approximation Algorithms for
NonSingleminded ProfitMaximization Problems with Limited Supply
(with Khaled Elbassioni
and Mahmoud Fouz). Proceedings of WINE 2010, pages 462472. ps or pdf. 
Approximability of the
Firefighter Problem: Computing Cuts over Time
(with Elliot Anshelevich,
Deeparnab Chakrabarty and Ameya Hate). Algorithmica, 62(12):520536, 2012. Preliminary version appeared as "Approximation Algorithms for the Firefighter Problem: Cuts over Time and Submodularity" in Proceedings of ISAAC 2009, pages 974983. Journal version ps, pdf or conference version ps, pdf. 
Approximation Algorithms for
Singleminded Envyfree Profitmaximization Problems with Limited Supply
(with Maurice Cheung). Proceedings of FOCS 2008, pages 3544. ps or pdf. Slides: Long version (ppt). Presented at the Caltech CMI 5th Anniversary Workshop (invited talk), November 2009; CORSINFORMS International Meeting (invited talk), June 2009; Theory seminar at SUNY Buffalo, August 2009; Eastern Great Lakes Theory Workshop, September 2008; Tutte seminar at the University of Waterloo, September 2008. 
Approximation Algorithms for Labeling
Hierarchical Taxonomies
(with Yuval Rabani
and Leonard Schulman). Proceedings of SODA 2008, pages 671680. ps or pdf. 
Truthful Mechanism Design for
Multidimensional Scheduling via Cycle Monotonicity
(with Ron Lavi). Games and Economic Behavior, 67(1):99124, 2009. Special issue devoted to selected papers from EC 2007. Preliminary version in Proceedings of EC 2007, pages 252261. Journal version ps, pdf or conference version ps, pdf. 
The Effectiveness of Stackelberg
Strategies and Tolls for Network Congestion Games. ACM Transactions on Algorithms, 8(4):36, 2012. Preliminary version appeared in Proceedings of SODA 2007, pages 11331142. Journal version ps, pdf or conference version ps, pdf. Slides: Short version (ppt). Presented at SODA, January 2007. 
Approximation Algorithms for
Prize Collecting Steiner Forest Problems with Submodular Penalty Functions
(with Yogeshwer Sharma
and David Williamson). Proceedings of SODA 2007, pages 12751284. ps or pdf. Slides: Long version (ppt). Presented at the Combinatorial Optimization Seminar at the University of Waterloo, February 2007. 
The Effectiveness of LloydType Methods
for the kMeans Problem
(with Rafail Ostrovsky,
Yuval Rabani and
Leonard Schulman). Journal of the ACM, 59(6):28, 2012. Preliminary version appeared in Proceedings of FOCS 2006, pages 165174. Journal version ps, pdf or conference version ps, pdf. Slides: Long version (ppt) or short version (ppt). Presented at FOCS, October 2006; Algorithms and Complexity Seminar at University of Waterloo, November 2006. 
Approximation Algorithms for Graph Homomorphism Problems
(with Michael Langberg and
Yuval Rabani). Proceedings of APPROX 2006, pages 176187. ps or pdf. Slides: Long version (ppt). Presented at the Combinatorial Optimization Seminar at the University of Waterloo, November 2006. 
Approximation Algorithms for 2Stage Stochastic
Optimization Problems
(with David Shmoys). Survey article in ACM SIGACT News, 37(1):3346, March 2006. ps or pdf. See also a (slightly) shorter survey that appeared in Proceedings of FSTTCS 2006,pages 519. ps or pdf. Slides (ppt) from a survey talk given at the Aladdin Workshop on Flexible Network Design , November 2005. 
Truthful and Nearoptimal
Mechanism Design via Linear Programming
(with Ron Lavi). Journal of the ACM, 58(6):25, 2011. Preliminary version appeared in Proceedings of FOCS 2005, pages 595604. Journal version ps, pdf or conference version ps, pdf. Slides: Long version (ppt) or a (slightly) shorter version (ppt). Presented at FOCS, October 2005; Theory seminars at Caltech, November 2005 and IBM Yorktown Heights, December 2005; Tutte seminar at the University of Waterloo, November 2006; INFORMS Annual Meeting (invited talk), November 2007. 
Samplingbased Approximation
Algorithms for Multistage Stochastic Optimization
(with David Shmoys). SIAM Journal on Computing, 41(4):9751004, 2012. Preliminary version appeared in Proceedings of FOCS 2005, pages 357366. Journal version ps, pdf or conference version ps, pdf. Note: There was a subtle error in the definition of the grid in the conference version, which has been corrected in the detailed version posted above. This error has also been corrected in the unpublished manuscript below on "The Sample Average Approximation Method for 2stage Stochastic Optimization". Slides: Long version (ppt) or a (slightly) shorter version (ppt). Presented at FOCS, October 2005; Oberwolfach Workshop on Combinatorial Optimization, November 2005; Dagstuhl Workshop on Probabilistic Methods in the Design and Analysis of Algorithms, October 2007. 
The Sample Average Approximation Method for 2stage Stochastic
Optimization
(with David Shmoys). Unpublished manuscript, 2004. ps or pdf. 
Network Design for Information Networks
(with Ara Hayrapetyan and
Éva Tardos). Proceedings of SODA 2005, pages 933942. ps or pdf. Note: On the last page, the paper incorrectly claims that the GoemansWilliamson primaldual algorithm for PCST yields a 2approximation algorithm for PCST with submodular penalties. In fact, this only yields a 3approximation algorithm. (A slightly better guarantee can be obtained via LP rounding; see the paper with Yogeshwer Sharma and David Williamson above.) Slides: Short version (ppt). Presented at the Bertinoro Workshop on Models and Algorithms for Information Networks (MAIN), October 2004; INFORMS Annual Meeting (invited talk), November 2005. 
An Approximation Scheme for Stochastic Linear
Programming and its Application to Stochastic Integer Programs
(with David Shmoys). Journal of the ACM, 53(6):9781012, 2006. Preliminary version appeared as "Stochastic Optimization is (almost) as Easy as Deterministic Optimization" in Proceedings of FOCS 2004, pages 228237. (Invitation to special issue of SIAM Journal on Computing declined.) Journal version ps, pdf or conference version ps, pdf. See also my PhD thesis. Slides: Long version (ppt) or short version (ppt). Presented at Cornell University; CMI Fall 2004 Retreat; 10th International Conference on Stochastic Programming (SPX), 2004; FOCS 2004; Dagstuhl Seminar on Algorithms for Optimization with Incomplete Information, 2005; Theory and IEOR seminars at the University of Rome "La Sapienza", MIT, Brown University, IBM Yorktown Heights, Columbia University. 
Optimal Powerdown Strategies
(with John Augustine and
Sandy Irani). SIAM Journal on Computing, 37(5):14991516, 2008. Preliminary version appeared in Proceedings of FOCS 2004, pages 530539. Journal version ps, pdf or conference version ps, pdf. Slides: Short version (ppt). Presented at FOCS, Rome, October 2004. 
Approximation Algorithms for
Data Placement Problems
(with Ivan Baev and
Rajmohan Rajaraman). SIAM Journal on Computing, 38(4):14111429, 2008. Merger of two papers: "Approximation Algorithms for Data Placement in Arbitrary Networks", SODA 2001, and an unpublished manuscript, "Algorithms for Data Placement Problems", 2004. Journal version ps or pdf. 
LPbased Approximation Algorithms for
Capacitated Facility Location
(with Retsef Levi and
David Shmoys). Mathematical Programming, 131(12):365379, 2012. Preliminary version appeared in Proceedings of IPCO 2004, pages 206218. Journal version ps, pdf or conference version ps, pdf. Slides: Short version (ppt). Presented at IPCO, New York, June 2004. 
Correlation Clustering: Maximizing Agreements via
Semidefinite Programming. Proceedings of SODA 2004, pages 519520. ps or pdf. Won the Best Student Paper Award. Slides: Short version (ppt). Presented at the Theory Seminar at Cornell, November 2003 and at SODA, New Orleans, January 2004. 
Facility Location with Service Installation Costs
(with David Shmoys and
Retsef Levi). Proceedings of SODA 2004, pages 10811090. ps or pdf. Slides: Short version (ppt). Presented at SODA, New Orleans, January 2004. 
FaultTolerant Facility Location
(with David Shmoys). ACM Transactions on Algorithms, 4(4), article no. 51, 2008. Preliminary version appeared in Proceedings of SODA 2003, pages 735736. Journal version ps, pdf or conference version ps, pdf. Slides: Long version (ppt) or short version (ppt). Presented at the Theory Seminar at Cornell, April 2002 and at SODA, Baltimore, January 2003. 
PrimalDual Algorithms for Connected Facility Location
Problems
(with Amit Kumar). Algorithmica, 40(4):245269, 2004. Special issue devoted to selected papers from APPROX 2002. Preliminary version in Proceedings of APPROX 2002, pages 256269. Journal version ps, pdf or conference version ps, pdf. Slides: Long version (ppt) or a (slightly) shorter version (ppt). Presented at the Algorithms Seminar at the MaxPlanckInstitut für Informatik, Saarbrücken, August 2002; APPROX, Rome, September 2002; Theory Seminar at Cornell, October 2002; Integrated Logistics Workshop (an ALADDIN PROBE) at Princeton, October 2002. 
A Randomized Algorithm for Flow Shop Scheduling
(with Naveen Garg and
Sachin Jain). Proceedings of FSTTCS 1999, pages 213218. ps or pdf. 
Approximation Algorithms for
Clustering Problems. PhD Thesis, Dept. of Computer Science, Cornell University, May 2004. ps or pdf. Note: There was a small error in Lemma 2.4.1 in the earlier version. As a result, one has to use a slightly different clusterselection rule in the demandoblivious primalrounding algorithm, and the approximation factor increases to 1.858. This correspondingly affects the approximation ratios of the algorithms for 2stage stochastic UFL (Chapter 4), and 2stage stochastic FLSIC (Section 5.6). The version posted here is the corrected version. 
Improving the Quality vs. Time Ratio of GraphCut Based Algorithms for Visual
Correspondence. Unpublished manuscript, 2002. 
Scheduling Algorithms. Undergraduate (B. Tech.) Thesis, Dept. of Computer Science, Indian Institute of Technology, Delhi, May 1999. 