This paper presents a new approach to solving the optimal unit location problem in a stochastic emergency service system that takes into account state transitions and unit availabilities. The goal is to minimize the system-wide mean response time, which is formulated as a combinatorial optimization problem. We show that this problem is NP-hard and develop lower and upper bounds for the optimal solution using a special case of the classic p-median problem. To solve the problem, we develop a Bayesian optimization algorithm that we show converges to the optimal solution with a sublinear regret rate. Through numerical experiments and a study utilizing real data from the St. Paul, Minnesota emergency response system, we demonstrate that our model consistently and efficiently converges to the optimal solution. This is in contrast to the performance of the p-median, which deteriorates with increased utilizations. Our solution can potentially serve as a practical tool for emergency unit deployment decisions and is applicable in large cities.
Hola!
You have landed on the personal website of Yi Zhang, an academic researcher at the intersection of decision-making, machine learning, and stochastic modeling, working on utilizing learning & optimization tools to revolutionize the way we understand the world and create tangible impacts. On the applied side, I am interested in healthcare, service operations management, and AI for science.
Currently I am a first-year master student majoring in Management Science & Engineering @ Tsinghua and Operations Research @ Columbia. I am extremely fortunate to be advised by Cheng Hua and Yong Liang, and to work closely with Xi Chen, Elynn Chen, and Stefanus Jasin.
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Note1 : I'm actively seeking Ph.D. position in Operations Research or Operations Management (OR/OM) for Fall 2026. Feel free to contact me at anytime.
Education Background
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Sep 2025 – Jun 2026 (expected)
Columbia University, Fu Foundation School of Engineering
-New York, USA
-M.S. in Operations Research
Tsinghua-Columbia Dual Master’s Degree in Business Analytics
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Sep 2024 – Jun 2026(expected)
Tsinghua University, School of Economics and Management
-Beijing, China
-M.S. in Business Analytics
Courses: Stochastic Process (PhD level), Convex Optimization (PhD level), Advanced Operations Research (PhD level), Data Analytics: Inference and Decision Making, Advanced Econometrics, Advanced Machine Learning (PhD level)
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Sep 2020 – Jun 2024
Tongji University, School of Economics and Management
-Shanghai, China
-B.S. in Management Information System
GPA:4.92/5 (Rank: Top 1%, Graduation with the Highest Honor)
Courses: Calculus, Discrete mathematics, Linear Algebra, Probability Theory, Applied Statistics, Data Structure, Data Science, Business Modeling and Simulation, Database Technology (All A+)
Research Interest
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My research interests lie at the intersection of adaptive sequential decision-making, stochastic modeling and Bayesian non-parametric model, especially Gaussian process, with applications in healthcare delivery, AI for science and service operations management. These fields hold immense societal significance, offering the potential to revolutionize the way we understand and solve critical challenges. I'm dedicated to taking the power I have been given and use it for this meaning cause, aspiring to leave this world better than I found it.
--"What's important in life?"
--"To improve the human condition; to positively affect the lives of people, especially young people; and to increase the human understanding of how the world works."
Professional Experience
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Jul 2023 – Nov 2023
Bosch, Corporate Research
-Shanghai, China
-Data Scientist Intern
Build a LSTM network to predict cross-selling probability by purchasing sequence. (Patents Pending)
Use SQL to fetch data and PowerBI to perform visualization; Use Jingdong Shufang to review sales performance. -
Jan 2023 – Mar 2023
SAP, Data Intelligence Office
-Shanghai, China
-Data Modeling and Predictive Analysis Intern
Develop a tool to monitor the backstage data loading process and analyze the error information.
Write 6 technical docs about development work; responsible for ticket processing; assist scrum master in project planning -
July 2022 – Sept. 2022
Deloitte, Risk Consulting Department
-Chongqing, China
-Quant Researcher Assistant
Use OCR and Python to capture government’s financial data; check data reliability by government budget equation.
Participate in the construction of factors like government fiscal impact, and city primacy to enrich the factor pool.
Honors & Awards
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Graduation with the Highest Honor: Outstanding Undergraduate of Shanghai
2024National Scholarship (Top 0.2% scholarship from Ministry of Education of China)
2021 & 2022Rongfang Shen Scholarship (Top 1% in Tongji University)
2021
Recent Updates
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Feb 2025: Our paper "Demystifying the Dimensions and Roles of Metaverse Gaming Experience Value: A Multi-Study Investigation" has been published on Journal of Management Information System. My first journal article! June 2024: Graduate from Tongji University and is awarded Excellent Graduate of Class 2024. Highest honor for undergraduates in Shanghai! May. 2024: We will give a talk at Development of Management Science and Engineering Forum at Antai College of Economics and Management, Shanghai Jiao Tong University. Dec. 2023: We will give a talk about our work at pre-ICIS HCI research workshop. See you there! May 2023: Our paper "When Online Auction Meets Virtual Reality: An Empirical Investigation" has been accepted by SIGHCI 2023 Proceeding. A good start of my academic journey! Oct. 2022: Honored to be awarded the National Scholarship again! Oct. 2021: Honored to be awarded the National Scholarship. Highest academic honor from Ministry of Education of the People's Republic of China! June 2021: Big decision! Switching my major from Architecture and Urban Planning to Management Information System.
Working Papers
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Spectral Mixture Kernels for Bayesian Optimization
Bayesian Optimization (BO) is a well-established approach for solving expensive black-box optimization tasks. However, the selection of its underlying probabilistic surrogate model remains an important yet challenging problem. We introduce a novel Gaussian Process (GP)-based BO approach adopting spectral mixture kernels, derived from spectral densities which are scale-location mixtures of Cauchy and Gaussian distributions. It preserves the sample efficiency of BO, whist boosting expressiveness and flexibility of the GP surrogate. We further bound the maximal information gain of spectral mixture kernels in terms of operator spectra, and demonstrate that it is possible to approximate conventional kernels and their compositions using them. Finally, We empirically validate that our BO method outperforms current baselines on a variety of synthetic and real-world examples.
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Integrated Optimization of Service Routing and Scheduling in Home Healthcare
Traditional home health care (HHC) service system has long been faced with the problem of unnecessary waiting of both health care workers and customers. To facilitate medical resources utilization and customer satisfaction, this paper proposes a stochastic Vehicle Routing and Appointment Scheduling problem (VRASP) considering integrated optimization of routing and scheduled arrival time, incorporating various uncertainties under the scenario of HHC delivery. We formulate a mixed-integer nonlinear programming model with the constraints of time windows and working regulations and the objective function of minimizing total travel costs of the door-to-door service and waiting penalties. Employing Sample Average Approximation method, we estimate the expectation of objective function through Monte Carlo simulation, and design a Variable Neighborhood Search algorithm to solve the problem. We further validate the efficiency and effectiveness of the proposed algorithm through a comparison with CPLEX solver on various numerical cases. Results show that the proposed algorithm can provide high-quality solutions with short computing times.
Work in Progress
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LLM-based Automatic Heuristic Design for Inventory Management
Conducted an extensive literature review on Automatic Heuristic Design, analyzing cutting-edge methodologies such as EoH (Evolution of Heuristics) and ReEvo (Recursive Evolution) to identify optimization strategies.
Designed and implemented novel inventory and ordering policies by leveraging Base Stock, Capped Base Stock, and Constant Order as initial strategies, enhancing decision-making efficiency in supply chain model.
Developed data-driven heuristics through systematic experimentation, improving algorithmic performance in dynamic inventory management scenarios.
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Heterogeneous Multi-Market Cross-Product Transfer Dynamic Pricing in High Dimensions
Consider the problem of multi-product dynamic pricing with contextual information, where a seller is faced with a large number products which are described by high-dimensional feature vectors, and customers with unknown heterogeneous price sensitivities.
Propose a pricing policy that uses a regularized maximum likelihood function to estimate the parameters of the choice model and subsequently sets the best prices based on the obtained estimates.
Benchmark the performance using the classic regret minimization framework where the regret is defined as the expected revenue loss against a clairvoyant policy that knows the parameters of the choice model in advance, and establish a lower bound and upper bound on the regret.
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Automated Bayesian Optimization with Input Noise
Design an algorithm that dynamically selects the most promising kernel function based on model marginal likelihood to properly choose an surrogate model for Bayesian Optimization (BO), which is realized by initiating from an empty kernel and iteratively applying grammatical operations.
Explore the phenomenon of mismatching and overfitting in different Reproducing Kernel Hilbert Spaces to penalize the potential unmanageable hyperparameter inference induced by complicated compositions of kernels.
Propose a probabilistic formulation of objective function and acquisition function using (i) rejection sampling and (ii)expectation propagation, to identify optimal solutions under input noise.
Evaluate the proposed algorithm on several benchmark problems from the optimization literature. The results show that our algorithm reliably finds robust optima, outperforming existing methods on most benchmarks.
Miscellaneous
- My Chinese name is 张易. You can also call me Zoey.
- I play Chinese instruments since I was six, and acquired Graduate Performance Diploma in Guzheng.
- I spend almost all my vacations traveling and photographing.