Papers by Anna Timonina-Farkas
Journal of Intelligent Manufacturing, Sep 27, 2022
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Operations Research
Ranking algorithms play a crucial role in information technologies and numerical analysis due to ... more Ranking algorithms play a crucial role in information technologies and numerical analysis due to their efficiency in high dimensions and wide range of possible applications, including internet ranking, scientometrics, and systemic risk in finance (SinkRank and DebtRank). The traditional approach to internet ranking goes back to the seminal work of Sergey Brin and Larry Page, who developed the initial method PageRank (PR) in order to rank websites for search engine results based on linear algebra rules. But how robust is this method in times of rapid internet growth? Recent works have studied robust reformulations of the PageRank model for the case when links in the network structure may vary; that is, some links may appear or disappear, influencing the transportation matrix defined by the network structure. In this article, the authors make a further step forward, allowing the network to vary not only in links but also in the number of nodes. The authors focus on growing network str...
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Operations Research
Ranking algorithms play a crucial role in information technologies and numerical analysis due to ... more Ranking algorithms play a crucial role in information technologies and numerical analysis due to their efficiency in high dimensions and wide range of possible applications, including internet ranking, scientometrics, and systemic risk in finance (SinkRank and DebtRank). The traditional approach to internet ranking goes back to the seminal work of Sergey Brin and Larry Page, who developed the initial method PageRank (PR) in order to rank websites for search engine results based on linear algebra rules. But how robust is this method in times of rapid internet growth? Recent works have studied robust reformulations of the PageRank model for the case when links in the network structure may vary; that is, some links may appear or disappear, influencing the transportation matrix defined by the network structure. In this article, the authors make a further step forward, allowing the network to vary not only in links but also in the number of nodes. The authors focus on growing network str...
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Production and Operations Management
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Computational Management Science
Years of globalization, outsourcing and cost cutting have increased supply chain vulnerability ca... more Years of globalization, outsourcing and cost cutting have increased supply chain vulnerability calling for more effective risk mitigation strategies. In our research, we analyze supply chain disruptions in a production setting. Using a bilevel optimization framework, we minimize the total production cost for a manufacturer interested in finding optimal disruption mitigation strategies. The problem constitutes a convex network flow program under a chance constraint bounding the manufacturer’s regrets in disrupted scenarios. Thus, in contrast to standard bilevel optimization schemes with two decision-makers, a leader and a follower, our model searches for the optimal production plan of a manufacturer in view of a reduction in the sequence of his own scenario-specific regrets. Defined as the difference in costs of a reactive plan, which considers the disruption as unknown until it occurs, and a benchmark anticipative plan, which predicts the disruption in the beginning of the planning ...
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This contains all the codes and test data for the purpose of conducting <br> numerical test... more This contains all the codes and test data for the purpose of conducting <br> numerical tests on the algorithms developed for SNSF project 100018_179272.
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Approximation techniques are challenging, important and very often irreplaceable solution methods... more Approximation techniques are challenging, important and very often irreplaceable solution methods for multi-stage stochastic optimization programs. Applications for scenario process approximation include financial and investment planning, inventory control, energy production and trading, electricity generation planning, pension fund management, supply chain management and similar fields. In multi-stage stochastic optimization problems the amount of stage-wise available information is crucial. While some authors deal with filtration distances, in this paper we consider the concepts of nested distributions and their distances which allows to keep the setup purely distributional but at the same time to introduce information and information constraints. Also we introduce the distance between stochastic process and a tree and we generalize the concept of nested distance for the case of infinite trees, i.e. for the case of two stochastic processes given by their continuous distributions. ...
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European Journal of Operational Research
Abstract Assortment planning deserves much attention from practitioners and academics due to its ... more Abstract Assortment planning deserves much attention from practitioners and academics due to its direct impact on retailers’ commercial success. In this paper we focus on the increasingly popular retail practice to use combined product assortments with both “standard” and more fashionable and short-lived “variable” products for building up store traffic of “loyal” and “non-loyal” heterogeneous customers and enlarging the sales due to the potential cross-selling effect. Addressing the assortment planning as a bilevel optimization problem, we focus on decision-dependent uncertainties: the retailer’s binary decision about product inclusion influences the distribution of the product’s demand. Furthermore, our model accounts for customers’ optimal purchase quantities, which depend on budget constraints limiting the basket that a customer is able to purchase. We propose iterative heuristics using optimal quantization of demand and customers budget distributions to define the total assortment and the inventory level per product. These heuristics provide lower bounds on the optimal value. We conduct a comparison to other existing lower bounds and we formulate upper bounds via linear (LP) and semidefinite (SDP) relaxations for the performance evaluation of the heuristics and for an efficient numerical solution in high-dimensional cases. For managerial insights, we compare the proposed approach with three assortment planning strategies: (1) the retailer does not carry variable products; (2) the retailer ignores the cross-selling effect; and (3) the maximum space allocated to each product is fixed. Our results suggest that variable assortment boosts the retailers profits if the cross-selling effect is not neglected in the decision about products quantities.
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Computational Management Science
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Insurance: Mathematics and Economics, 2017
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Multi-stage stochastic optimization is a well-known quantitative tool for decision-making under u... more Multi-stage stochastic optimization is a well-known quantitative tool for decision-making under uncertainty, which applications include financial and investment planning, inventory control, energy production and trading, electricity generation planning, supply chain management and similar fields. Theoretical solution of multi-stage stochastic programs can be found explicitly only in very exceptional cases due to the complexity of the functional form of the problems. Therefore, the necessity of numerical solution arises. In this article, we introduce a new approximation scheme, which uses optimal quantization of conditional probabilities instead of typical Monte-Carlo simulations and which allows to enhance both accuracy and efficiency of the solution. We enhance accuracy of the estimation by the use of optimal distribution discretization on scenario trees, preserving efficiency of numerical algorithms by the combination with the backtracking dynamic programming. We consider optimali...
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Quantitative Finance and Economics
The COVID-19 pandemic has demonstrated the importance and value of multi-period asset allocation ... more The COVID-19 pandemic has demonstrated the importance and value of multi-period asset allocation strategies responding to rapid changes in market behavior. In this article, we formulate and solve a multi-stage stochastic optimization problem, choosing the indices' optimal weights dynamically in line with a customized data-driven Bellman's procedure. We use basic asset classes (equities, fixed income, cash and cash equivalents) and five corresponding indices for the development of optimal strategies. In our multi-period setup, the probability model describing the uncertainty about the value of asset returns changes over time and is scenario-specific. Given a high enough variation of model parameters, this allows to account for possible crises events. In this article, we construct optimal allocation strategies accounting for the influence of the COVID-19 pandemic on financial returns. We observe that the growth in the number of infections influences financial markets and makes assets' behavior more dependent. Solving the multi-stage asset allocation problem dynamically, we (i) propose a fully data-driven method to estimate time-varying conditional probability models and (ii) we implement the optimal quantization procedure for the scenario approximation. We consider optimality of quantization methods in the sense of minimal distances between continuous-state distributions and their discrete approximations. Minimizing the well-known Kantorovich-Wasserstein distance at each time stage, we bound the approximation error, enhancing accuracy of the decision-making. Using the first-stage allocation strategy developed via our method, we observe ca. 10% wealth growth on average out-of-sample with a maximum of ca. 20% and a minimum of ca. 5% over a three-month period. Further, we demonstrate that monthly reoptimization aids in reducing uncertainty at a cost of maximal wealth. Also, we show that optimistically offsetted distribution parameters lead to a reduction in out-of-sample wealth due to the COVID-19 crisis.
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SSRN Electronic Journal
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SSRN Electronic Journal
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Risk Analysis, 2015
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Papers by Anna Timonina-Farkas