Todor Stoilov

Todor Stoilov
Bulgarian Academy of Sciences | BAS · Department of Hierarchical Systems

Eng. Ph.D., D.Sc.

About

156
Publications
44,341
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
526
Citations
Additional affiliations
June 2009 - present
Bulgarian Academy of Sciences
Position
  • Professor (Full)

Publications

Publications (156)
Article
Inventory optimization is extended with additional constraints that affect production efficiency using estimated inventory. The extension of the inventory problem is in a special formal form with an additional optimization problem. The latter is aimed at minimizing production costs while using optimal volumes of material stocks. Such integration of...
Article
A bi-level problem is defined for the optimization of inventory management. This formalization allows the simultaneous delivery of different types of goods according to the required volume of consumption for the production of goods. The resources, which are supplied are strictly related to the production volumes, which minimize the inventory costs....
Article
Full-text available
Electrical energy management of an organization is related to the appropriate planning of required payments and allocation of resources accordingly. It is important for good management to account for past costs and to forecast future costs. An intelligent solution for the mathematical formalization of this process is presented in the study. The res...
Article
Full-text available
The paper aims to solve the problem of reallocating financial payments between disbursements and outflows by increasing the efficiency of working capital. The reallocation of financial payments is a different case from the reallocation of investments. The disbursements can be regarded as a set of assets, which generate negative returns in compariso...
Article
Full-text available
The main control tool for traffic management in urban areas is traffic light settings. The goal is to decrease the queue lengths at intersections. Usually, the duration of the green light of the traffic light is used for control. The control approach is based on the so-called “store-and-forward” model. However, this model does not reflect the stoch...
Article
Full-text available
Logistic tasks are aimed at the optimal distribution of material, energy, financial and human resources. This research has a narrow field aimed at optimal management of financial resources and their redistribution. Specifically, a reinvestment policy model is derived by maximizing the profit of a business entity. Reinvestment is done with risk-free...
Article
Full-text available
An optimization model for traffic light control in an urban network of intersections is derived. The model is based on store-and-forward analytic relations, which account for the length of the queue of waiting vehicles in front of the traffic light intersection. The model is complicated with probabilistic relations that formalize the requirements f...
Article
Full-text available
An algorithm is derived for active business management. The key component of the algorithm is the definition and solution of an appropriate portfolio problem. For the last one, the disbursements for the business management are regarded as potential portfolio resources. For the portfolio definition, the increases or decreases of the disbursements ar...
Article
Full-text available
The husbandry management is assessed in general by comparison of current and past economical results, which are used as a universal business metric. Sustainable management in general targets minimization of risk and maximization of the return for managing business activities. The minimization of the economic risk allows for decreasing the potential...
Conference Paper
The control object is the urban traffic of network of eight crossroad sections as a part of density populated area in Sofia. The goal is minimization of vehicle queue lengths in front of the junctions, which leads to faster driving, reducing the air and noise pollution and better ecological picture. The paper analyzes two types of modeling and opti...
Conference Paper
The paper gives a practical example for the information and computer support in a decision making process about investments on real estate market. The computer support is based on considerable quantitative evaluations of market characteristics about real estates. These computations are based on the usage of a portfolio theory, which is adapted in t...
Article
Full-text available
A bi-level model for traffic signal optimization is developed. The model predictive framework is applied for traffic control in an urban traffic network. The potential of the bi-level formalization is used to increase the space of control influences with simultaneous evaluation of the green light and cycle durations. Thus, the increased control spa...
Article
Full-text available
An active policy for portfolio optimization is developed based on repetitive application of modified Black-Litterman (BL) portfolio model and new formal definition of the expert views. New subjective views are defined which are based on the differences between the historical mean asset returns and their implied return values. An algorithm for the i...
Article
Full-text available
An investment policy is suggested about assets on real estate markets. Such analysis recommends investments in non-financial assets and optimization of the results from such decisions. The formalization of the investment policy is based on the portfolio theory for asset allocation. Two main criteria are applied for the decision making: return and r...
Article
Full-text available
An algorithm is derived for the development of portfolio decision-support information service. The algorithm allows being automated evaluations for the definition and solution of portfolio problems. Small set of historical data of asset returns with limited set of assets are used for the portfolio, which is the case for no institutional portfolio m...
Article
Full-text available
The urban traffic control optimization is a complex problem because of the interconnections among the junctions and the dynamical behavior of the traffic flows. Optimization with one control variable in the literature is presented. In this research optimization model consisting of two control variables is developed. Hierarchical bi-level methodolog...
Book
Full-text available
The goal of this study is to use an MMUM mathematical model updating method from incomplete test data to detect damages in reinforced concrete bridges. It is carried out a suitable finite element model of a repaired bridge. We can use the diagnostics to find and detect damage in a reinforced concrete bridge. As a result, modal testing techniques ha...
Article
Full-text available
The paper realizes inclusion of probabilistic measure for risk, VaR (Value at Risk), into a portfolio optimization problem. The formal analysis of the portfolio problem illustrates the evolution of the portfolio theory in sequentially inclusion of different market characteristics into the problem. They make modifications and complications of the po...
Article
Full-text available
The mean-variance (MV) portfolio optimization targets higher return for investment period despite the unknown stochastic behavior of the future asset returns. That is why a risk is explicitly considering, quantified by algebraic characteristics of volatilities and co-variances. A new probabilistic definition of portfolio risk is the Value at Risk (...
Chapter
The portfolio optimization is a complex task, addressing decision making of financial investments. A requirement for the portfolio management is to deal with a lot of securities, traded on the stock exchange, frequently containing hundreds of stocks and securities. The modern portfolio theory insists to be defined a portfolio optimization problem,...
Article
Full-text available
A quantitative analysis of the financial state of an animal husbandry is performed. The paper illustrates the usage of different economical parameters in order to present operational state of the husbandry and to search regularities for future actions. The added value of this research is the application of intelligent instruments in the management...
Article
Full-text available
The paper derives an evaluation algorithm for decreasing the computational workload in definition and solution of portfolio optimization problem. The algorithm applies numerical relations, which lead to transformation of the classical portfolio problem to optimization one, which contains parameters from Capital Market Theory. The decrease of the co...
Article
Full-text available
The paper makes analytical overviews of the Markowitz portfolio and the Capital Asset Pricing models and motivates the advances of the Black-Litterman (BL) one. This overview implies that for a small set of assets the BL model needs the characteristics of a specific market point, which cannot be taken from a global market index. The paper derives a...
Article
Full-text available
Application of the Portfolio theory to appreciation of the Bulgarian stock exchange following the most popular financial indices is presented. The data of these indices corresponds to the same watching periods an year before. Comparison of the optimization problem’s solutions and analysis of the financial activities are commented. Modification of t...
Conference Paper
The modern portfolio theory applies many computations, needed for assessment of investment policies of financial assets. The optimal portfolio decisions are based on quantitative evaluations, following numerical models and formal relations. Thus, applied computing supports the financial decisions. Without informatics tools and computational environ...
Conference Paper
The information services are widely used in virtual environments. As information services a lot of business entities operate offering e-shop facilities, virtually offering of business information, galleries, many others information services based on distribution of on-line important data. The human requirements to the information services increase...
Conference Paper
Information technology implements its outcomes in development information services, which are available in virtual environments. The increase of usage of information services insists on the functionalities, offering by the information systems to provide complex treatment of the data. Thus, additional and new business relations are identified and ca...
Chapter
The article examines the design and implementation of the “moving average” procedure in the structure of FPGAs. It demonstrates that its implementation in the form of a recursive filter and the use of the DSP48A1 digital signal processing unit, embedded in the Xilinx Spartan 6 FPGA series, guarantee minimal logical resources. An estimation of the s...
Article
Full-text available
The general contribution of this research is the implementation of new formal type of relative view, which has been added to the Black-Litterman Model (BLM) for asset management. It is well known that the BLM integrates both historical data about the assets’ returns and subjective views given by experts and investors. Such complicated model is expe...
Article
Full-text available
The increase of the utilization of public rail transportations is searched in directions for redistribution of the passenger travels between rail and bus transportation. The rail transport benefits by redistribution of the transportation flows on paths, predominantly supported by rails. The redistribution of the transportation is formalized by bi-l...
Article
Full-text available
The Intelligent Transportation System (ITS) is used as a term for integrating requirements and functionalities towards transportation systems, which in urban environment raises complex exploitation and control problems. Important part of the ITS is the control which has to be applied for traffic flows. The control processes are strongly linked with...
Article
Full-text available
The paper defines and solves a Linear-Quadratic-Gaussian (LQG) optimization problem addressing real time control policy of Urban Transportation Network (UTN). The paper presents UTN model definition, analysis and LQG optimization problem definition, resulting in special problem structure. A real application for UTN situated in Sofia, Bulgaria along...
Chapter
This chapter illustrates the ideas of multilevel system theory in the design of a traffic control system that embodies self-optimization properties. These ideas are described in terms of multilevel optimization problems. A simulation example is provided, explaining the methodology of multilevel optimization. The example shows the optimal control ev...
Chapter
The paper applies new formalization for the control of urban transportation. Bi-level optimization problem is defined, which is a different way to control simultaneously the traffic flows and traffic lights. The bi-level optimization problem uses the well known relations based on the store-and-forward modeling. However, the bi-level approach adds a...
Conference Paper
Full-text available
The formal approaches for the control of transportation systems are categorized mainly in two general formal descriptions:-Store and forward modeling;-Free way traffic control on high ways. These two families of models have their domain applications as noted above for urban transportation networks and for high way system of transport network. But t...
Article
Full-text available
This paper applies a bi-level formalism for the optimal control of an urban transportation network. The well known store-and-forward model in traffic control is utilized in order to increase the control space of the optimization problem. Mainly, the store-and-forward models apply the split as a control argument, assuming the traffic light cycle as...
Article
Full-text available
The operation of a complex system like a transportation network is considered with respect to the opportunities to identify the application of autonomic properties. The autonomic features of self-properties are analyzed. A multilevel approach is suggested for the formalization of the transport operation. The integration of relevant optimization pro...
Conference Paper
Web sites, which enable watching video clips online, have become very popular nowadays. One of the main problems with regard to that is the highly increasing workload of the machines that support those sites. The text describes the structure of Apache HTTP Server and focuses on the parameters that influence the efficiency of its usage. It also care...
Conference Paper
A bi-level optimization problem is defined for controlling an arterial corridor of traffic network. The hierarchical relations between two optimization problems allow optimizing two types of control variables: the split of green duration and the cycle time of the traffic lights. The benefit of the bi-level formulation has been identified and assess...
Chapter
The portfolio optimization theory targets the optimal resource allocation between sets of securities, available at the financial markets. Thus, the investment process is a task, which targets the maximization of the portfolio return and minimization of the portfolio risk. Because such an optimization problem becomes multi-criterion optimization one...
Conference Paper
Full-text available
An analysis of the potential formalism, used in the hierarchical system theory is performed, addressing the autonomic computing system design. In that manner, self management of the overall autonomic system can be achieved by influencing the local resources and the goals of the local computing subsystems. Thus, a quantitative formalization of the c...
Conference Paper
The portfolio optimization is implemented as e-service through Internet. Four-tier client-server model of WAN-based information system is designed satisfying the intersection of several domains: financial investments, optimization theory and information technologies.
Article
The paper presents a bilevel optimization problem, solved by a noniterative coordination method founded on the approximation of inexplicit upper level optimization problem to well defined analytical problem. The coordination problem founds on ldquoproposition - correctionrdquo operational algorithm which allows to perform limited data transfer betw...
Conference Paper
Full-text available
Information Systems Development is a process that needs not only technical capabilities but management capabilities as well. Managing successfully the development process creates a number of qualitative and quantitative benefits to all being involved (suppliers and customers). On the other hand, managing technical people can be both risky and diffi...
Article
Full-text available
Projects are living entities. They are born with the project idea and end with the project termination. The time in between can last for many years, in most of the cases, requiring continuous implementation and management effort. Over the time project changes on requirements change the implementation process and in turn the management process, the...
Conference Paper
Full-text available
Process development and standardization is considered the ability to reproduce the consistent high quality levels of a service or a product with the ability to develop optimum work methods or process and equipment conditions, to codify them, to be able to translate them into effective practices, and then to create the organizational circumstances t...
Article
The multilevel system theory applies two general methods of coordination, which influences the manner of subsystem management-goal and predictive coordinations. Both these general types of coordination perform multiple data transfer between the hierarchical levels and delay the evaluation and implementation of a global optimal solution of a control...
Conference Paper
Full-text available
An analysis of the general functions of the Enterprise Resource Planning (ERP) systems is performed. Historical development of ERP is given. Analysis and comparisons of three open source ERP are provided.
Article
The basic process principles are defined through the concept, values and theories of statistical control, which is used in many fields, regardless their type of operation. Processes development, maintenance, enhancement and management is not a formality issue for virtual organizational quality control and assurance. Process development and standard...
Article
Full-text available
In the last decades on the last century, applications of electromagnetic fields have increased both in number of them and in number of persons that use them. At the same time, a social worry regarding the use of these applications has spread. Some studies maintain that there is not any direct relation between electromagnetic field applications that...
Article
Full-text available
Application of workflow technologies in design and implementation of e-learning systems is considered. This is a technological solution for integrating e-learning resources and addressing e-learning applications. Examples of e-learning workflows are given. The main steps in developing e-learning systems based on workflow technologies are outlined.
Conference Paper
An analysis of the interactions between different resources in heterogeneous IT environment is given. The benefits of the Distributed Management Task Forces (DMTF) policies are assessed. The object-oriented information model CIM (Common Information Model) is studied. The relation between CIM and its XML implementation was evaluated. Because non-uni...
Conference Paper
Full-text available
Computational efficiency of the evaluations is assessed with the number of floating point operations (flops) in MATLAB environment. The initial high order matrix is decomposed to smaller matrices and analytical relations are applied. The area of application of these analytical relations is estimated. This research addresses problems, related to the...
Article
The chapter describes the main stages of the development of a system, supporting the decision-making in e-portfolio investment optimization. The developments target the implementation of web based e-service application for financial assistance in the choice of investment strategy, according to the investor's preferences. The implementation of portf...
Article
Full-text available
This paper presents the workflow management systems as a tool for modelling, executing and monitoring e-business processes. The automation of processes and particular the business processes is done by workflow systems. There are two main groups of workflow technologies for the specification and execution of all workflows -choreography languages and...

Network