Multi-stage stochastic engine usage optimization for fighter jet fleet using nested decomposition algorithm

In this paper, we study multistage stochastic mixed-integer nonlinear programs (MS-MINLP). This general class of problems encompasses, as important special cases, multistage stochastic convex optimization with non-Lipschitzian value functions and multistage stochastic mixed-integer linear optimization. We develop stochastic dual dynamic programming (SDDP) type algorithms with nested decomposition, deterministic sampling, and stochastic sampling. The key ingredient is a new type of cuts based on generalized conjugacy. Several interesting classes of MS-MINLP are identified, where the new algorithms are guaranteed to obtain the global optimum without the assumption of complete recourse. This significantly generalizes the classic SDDP algorithms. We also characterize the iteration complexity of the proposed algorithms. In particular, for a (T+1)-stage stochastic MINLP satisfying L-exact Lipschitz regularization with d-dimensional state spaces, to obtain an varepsilon -optimal root node solution, we prove that the number of iterations of the proposed deterministic sampling algorithm is upper bounded by {mathcal {O}}((frac{2LT}{varepsilon })^d), and is lower bounded by {mathcal {O}}((frac{LT}{4varepsilon })^d) for the general case or by {mathcal {O}}((frac{LT}{8varepsilon })^{d/2-1}) for the convex case. This shows that the obtained complexity bounds are rather sharp. It also reveals that the iteration complexity depends polynomially on the number of stages. We further show that the iteration complexity depends linearly on T, if all the state spaces are finite sets, or if we seek a (Tvarepsilon )-optimal solution when the state spaces are infinite sets, i.e. allowing the optimality gap to scale with T. To the best of our knowledge, this is the first work that reports global optimization algorithms as well as iteration complexity results for solving such a large class of multistage stochastic programs. The iteration complexity study resolves a conjecture by the late Prof. Shabbir Ahmed in the general setting of multistage stochastic mixed-integer optimization.

This work presents an implementation of a Nested Decomposition Algorithm (NDA) applied to co-optimizing generation and transmission capacity expansion planning problems in power systems, including operational flexibility constraints. The proposed methodology has been gaining relevance in recent years, as it can efficiently solve large mixed-integer problems faster than the conventional extensive formulation (mixed-integer linear programming). Three case studies are conducted on two IEEE test power systems to evaluate the algorithm’s performance and cut configuration. The first case study compares the performance between the NDA and the extensive formulation. The second case study compares the performance of each cut type, analyzing differences in simulation times and algorithm convergence. The third case study proposes a set of cut patterns based on the prior outcomes, whose performance and convergence are tested. Based on the simulation results, conclusions are drawn about the capability and performance of the NDA applied to the capacity expansion planning problem. The study shows that obtaining results with reasonable convergence in less simulation time is possible using a particular pattern.

In this paper, we consider multi-stage stochastic optimization problems with convex objectives and conic constraints at each stage. We present a new stochastic first-order method, namely the dynamic stochastic approximation (DSA) algorithm, for solving these types of stochastic optimization problems. We show that DSA can achieve an optimal $${{\mathcal {O}}}(1/\epsilon ^4)$$ rate of convergence in terms of the total number of required scenarios when applied to a three-stage stochastic optimization problem. We further show that this rate of convergence can be improved to $${{\mathcal {O}}}(1/\epsilon ^2)$$ when the objective function is strongly convex. We also discuss variants of DSA for solving more general multi-stage stochastic optimization problems with the number of stages $$T > 3$$ . The developed DSA algorithms only need to go through the scenario tree once in order to compute an $$\epsilon $$ -solution of the multi-stage stochastic optimization problem. As a result, the memory required by DSA only grows linearly with respect to the number of stages. To the best of our knowledge, this is the first time that stochastic approximation type methods are generalized for multi-stage stochastic optimization with $$T \ge 3$$ .

Multi-stage stochastic gradient method with momentum acceleration

In this paper, we show a significant role that geometric properties of uncertainty sets, such as symmetry, play in determining the power of robust and finitely adaptable solutions in multistage stochastic and adaptive optimization problems. We consider a fairly general class of multistage mixed integer stochastic and adaptive optimization problems and propose a good approximate solution policy with performance guarantees that depend on the geometric properties of the uncertainty sets. In particular, we show that a class of finitely adaptable solutions is a good approximation for both the multistage stochastic and the adaptive optimization problem. A finitely adaptable solution generalizes the notion of a static robust solution and specifies a small set of solutions for each stage; the solution policy implements the best solution from the given set, depending on the realization of the uncertain parameters in past stages. Therefore, it is a tractable approximation to a fully adaptable solution for the multistage problems. To the best of our knowledge, these are the first approximation results for the multistage problem in such generality. Moreover, the results and the proof techniques are quite general and also extend to include important constraints such as integrality and linear conic constraints.

The amount of stagewise available information is crucial in multistage stochastic optimization. But unlike data, which directly enter the profit&loss functions of a decision problem, information is invariant w.r.t. bijective transformations. The usual concept to deal with information in multistage stochastic programming is by introducing filtrations, i.e., increasing sequences of sigma-algebras, to which the decisions must be adapted. For the definition of filtrations one has to fix a certain probability space while random variables are typically given by their distributions only and all realizations of this distribution on some probability space are equivalent. We introduce here the new concept of nested distributions to describe the information structure as well as the scenario process of a stochastic optimization program in a way which is independent of specific versions of probability spaces and random variables. The setting is totally “in-distribution.” Two stochastic programs (with identical objective function and constraints) are equivalent if and only if the scenario processes have the same nested distribution. As a byproduct, we analyze the question of whether introducing extra randomness by defining randomized decisions would lead to improvement in the objective value. In the language of information this would mean that enlarging the filtration based on available information by (conditionally) independent additional random variables would have a positive effect. We show that, in general, the answer is yes, while for compound convex objectives, the answer is no. Finally, we define a distance between nested distributions, which generalizes the well-known Kantorovich distance of probability distributions and demonstrates that this distance may be used in quantifying the quality of approximation between a continuous stochastic program and a tree discretization, or between two tree discretizations.

Deterministic electric power infrastructure planning: Mixed-integer programming model and nested decomposition algorithm

Solving a stochastic inland waterway port management problem using a parallelized hybrid decomposition algorithm

To solve multistage adaptive stochastic optimization problems under both endogenous and exogenous uncertainty, a novel solution framework based on robust optimization technique is proposed. The endogenous uncertainty is modeled as scenarios based on an uncertainty set partitioning method. For each scenario, the adaptive binary decision is assumed constant and the continuous variable is approximated by a function linearly dependent on endogenous uncertain parameters. The exogenous uncertainty is modeled using lifting methods. The adaptive decisions are approximated using affine functions of the lifted uncertain parameters. In order to demonstrate the applicability of the proposed framework, a number of numerical examples of different complexity are studied and a case study for infrastructure and production planning of shale gas field development are presented. The results show that the proposed framework can effectively solve multistage adaptive stochastic optimization problems under both types of uncertainty.

We consider barrier problems associated with two and multistage stochastic convex optimization problems. We show that the barrier recourse functions at any stage form a selfconcordant family with respect to the barrier parameter. We also show that the complexity value of the flrst stage problem increases additively with the number of stages and scenarios. We use these results to propose a prototype primal interior point decomposition algorithm for the two-stage and multistage stochastic convex optimization problems admitting self-concordant barriers.

Aimed at sufficiently utilizing available data and prior distribution information, we introduce a data-driven Bayesian-type approach to solve multi-stage convex stochastic optimization, which can easily cope with the uncertainty about data process’s distributions and their inter-stage dependence. To unravel the properties of the proposed multi-stage Bayesian expectation optimization (BEO) problem, we establish the consistency of optimal value functions and solutions. Two kinds of algorithms are designed for the numerical solution of single-stage and multi-stage BEO problems, respectively. A queuing system and a multi-stage inventory problem are adopted to numerically demonstrate the advantages and practicality of the new framework and corresponding solution methods, compared with the usual formulations and solution methods for stochastic optimization problems.

The Dynamic Energy System Optimization Model (DESOM) was developed to investigate the roles of different technologies in the energy system over an extended period of time. The long-time horizon makes it possible to show phasing in and phasing out of capacity as well as exhaustion of resources. A preliminary version of DESOM had been created prior to the start of this project. The objectives of this project were to improve computational features of the program, to incorporate electric-sector detail into the existing version of DESOM, and to transfer the DESOM model to EPRI. DESOM was reformulated in a staircase structure and solved with a nested decomposition algorithm. Unfortunately, the resulting increase in model size negated the nested decomposition benefits. It was subsequently concluded that using commercial linear programming solution algorithms was the best option. A matrix and report generator software package, PDS/MaGen, was purchased to improve running of the model. The electrical sector was made more realistic by dividing the year into three seasons (winter, summer, spring/fall) and the day into two sections (day, night). The demands were then characterized by the time divison in which they occur. DESOM was transferred to EPRI.

Stochastic joint homecare service and capacity planning with nested decomposition approaches

: This paper presents a hybrid algorithm for multi-stage linear programs arising from time-phased or dynamic models. The hybrid computation is based on a nested decomposition algorithm and the revised simplex method. Initial computational experience is reported. (Author)

Multistage stochastic linear programs can represent a variety of practical decision problems. Solving a multistage stochastic program can be viewed as solving a large tree of linear programs. A common approach for solving these problems is the nested decomposition algorithm, which moves up down the tree by solving nodes and passing information among nodes. The natural independence of subtrees suggests that much of the computational effort of the nested decomposition algorithm can run in parallel across small numbers of fast processors. This paper explores the advantages of such parallel implementations over serial implementations and compares alternative sequencing protocols for parallel processors. Computational experience on a large test set of practical problems with up to 1.5 million constraints and almost 5 million variables suggests that parallel implementations may indeed work well, but they require careful attention to processor load balancing.