National Repository of Grey Literature 2 records found  Search took 0.00 seconds. 
Scenario generation methods for discrete data
Komora, Ondřej ; Procházka, Vít (advisor) ; Omelka, Marek (referee)
Stochastic optimization relies heavily on scenario generation, which has a large impact on the tractability of optimization methods and the quality of obtained solutions. Despite its importance, scenario generation for discrete data is rarely studied and even when it is, it often involves a problem-oriented method. However, the development of these methods is resource-intensive, resulting in a situation where viable easy-to-use alternatives to sampling are missing. In this work, we attempt to remedy the situation by proposing a new copula-based scenario generation method for discrete data. The method is based on extending discrete random variables and subsequent use of the so-called extension copula. We demonstrate the effectiveness of this method on the stochastic knapsack problem by using several metrics like in-sample stability, out-of-sample evaluation gap, and optimality gap. The results show that our method outperforms sampling and can serve as a more challenging benchmark for problem-oriented methods. 1
Sparse solutions in labeling optimization problems
Komora, Ondřej ; Branda, Martin (advisor) ; Lachout, Petr (referee)
The main goal of this work is to give self-contained description of proximal and ordi- nary stochastic subgradient descent methods, which are used in finding sparse solutions of labeling optimization problems. We will define and interpret necessary concepts lea- ding to the definition of those methods and we will discuss in detail conditions, under which we show convergence of these methods to critical point. At the end, we will pre- sent a numerical experiment on concrete optimization task where we demonstrate use of these methods. In this experiment we will also show how a suitable choice of so called regularization can influence sparsity of solution of this particular task. 1

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