Current Organizations / Institutes

The organizations/institutes from the scholar's latest article


Tsvetelin Zaevski has a total of 15 co-authors. Here are the top co-authors by number of shared publications:


Latest Publications

  • Fractional-linear-transformation-based probability distributions: Properties, examples, Hausdorff saturation, and applications

    by Tsvetelin Zaevski, Nikolay Kyurkchiev

    Probability distributions defined on a bounded interval are essential tools in data science, engineering, and risk management. The most important practical reason for their existence is the need to model real-world phenomena that possess strict physical, logical, or economic boundaries. This paper introduces a new class of probability distributions based on the fractional linear transform applied to a distribution defined on the positive real half-line. Consequently, the distribution’s infinite support is mapped onto a bounded interval. We can assume without loss of generality that this interval is (0, 1). We first derive some general theoretical results for the probability density functions, quantile functions, and other probability properties. A duality between distributions is established. Consequently, we investigate several particular cases based on the gamma, inverse gamma, Rayleigh, and generalized inverse Gaussian distributions. The so-called saturation in the Hausdorff sense is discussed. It provides a first-order approximation of the cumulative distribution function to the Γ-shaped curve {(0, 0) → (0, 1) → (1, 1)}. Thus, it can be viewed as a break-even point and can be useful in economics, finance, risk management, and other natural sciences, such as chemistry, physics, meteorology, etc. We also investigate the maximum likelihood estimator and check its asymptotic properties, consistency, and stability. We apply this method, as well as the least-squares approach, to two empirical datasets: one for yield curves and another for unemployment insurance issues. The statistical results strongly confirm the usefulness of the proposed model.

  • Open Access

    On the put-call duality of the game options

    by Tsvetelin Zaevski

    The purpose of this paper is to obtain a duality between the game put and call options assuming three component penalties – proportion of the usual option payoff, shares of the underlying asset, and a fixed amount. We examine separately the cases of finite and infinite maturities. For the perpetual options, we need to derive a polynomial-style equations for the optimal boundaries. We prove the existence and uniqueness of their solutions as well as provide a method for their deriving. This result is important in itself since the current literature in the field is based on inverting of several functions or on solving of non-linear systems which may lead to some computational difficulties and significant errors for extreme parameter values. Furthermore, the duality is established under a finite time horizon too. It is important to note that this duality does not hold under the classical assumption of a fixed penalty.

  • Open Access

    Dynamics of a Modified Third–Order Phase–Locked Loops (PLL): Melnikov Approach, Simulations

    by Nikolay Kyurkchiev, Tsvetelin Zaevski, Anton Iliev, Vesselin Kyurkchiev, Asen Rahnev

    In this article, we investigate the dynamics of new modified third-order Phase-Locked Loops (PLLs). Our goal here is to investigate the effect of the new factor ∑j=1Najsin(jωt) on the dynamics of the proposed model. Using perturbation techniques based on Andronov–Melnikov concepts, we demonstrate that horseshoe chaos exists in three-dimensional nonautonomous systems. Several simulations are performed. Additionally, we present a few specific modules for examining the dynamics of the hypothetical oscillator circuit under consideration. This will be a crucial component of a much broader web-based scientific computing application. We will explicitly note that the proposed model is hypothetical and specialists working in this scientific field have a say. We will consider a numerical example of the possible application of the Melnikov function in the modeling of the radiation Melnikov antenna diagram. In addition, we examine a generalization based on probability distributions.

  • Open Access

    Studying Chaos in a Modified Dynamical Model: Some Applications

    by Tsvetelin Zaevski, Nikolay Kyurkchiev, Anton Iliev, Vesselin Kyurkchiev, Asen Rahnev

    Many authors consider modified SIQR (susceptible, infected, isolated (quarantined), and recovered individuals) models for childhood diseases. In this paper, we examine a modified differential system with N free parameters that may be of interest to epidemiology experts. We pay special attention to the Melnikov function, which corresponds to the proposed new model. We create the Melnikov equation (M(t)=0) and analyze all of its roots using a specially designed software program. This gives the researcher the chance to accurately comprehend and articulate the classical Melnikov criterion for the potential appearance of chaos in the dynamical system. Additionally, we present a few specific modules for examining the new model’s dynamics. Additionally covered is a potential use of the Melnikov function that corresponds to the differential model under consideration, with particular potential in the modeling and synthesis of antenna diagrams. Last but not least, we consider the proposed generalization from a stochastic point of view.

  • Open Access

    A Note on Chaos of a Modified Piecewise Linear Discontinuous System with Multiple-Well Potentials: Melnikov Approach with Simulations

    by Tsvetelin Zaevski, Nikolay Kyurkchiev, Anton Iliev

    The topic of chaotic thresholds for piecewise linear discontinuous (PWLD) systems with multiple-well potentials is a persistent topic in the research of a number of authors. In this article we investigate the chaos of a modified piecewise linear discontinuous (MPWLD) system. The model, containing N free parameters, could be of interest to specialists working in this area. With a specially developed software product, we generate the Melnikov equation M(t)=0 and examine all its zeros. This opens up an opportunity for researchers to correctly understand and formulate the classical Melnikov criterion for the possible occurrence of chaos in dynamical systems. Several simulations are composed. We also demonstrate some specialized modules for investigating the dynamics of the proposed model. Intriguing and new generalizations made through probabilistic constructions are considered.

  • Open Access

    Chaos in a Generalized Perturbed Lotka–Volterra Model

    by Nikolay Kyurkchiev, Tsvetelin Zaevski, Anton Iliev, Vesselin Kyurkchiev, Angel Golev, Asen Rahnev

    In this paper we investigate the chaos of a generalized perturbed Lotka–Volterra model based on considerations by other studies used in the literature. The model, containing N number of free parameters, could be of interest to specialists working in the fields of biological applications, chemistry, reaction kinetics, biostatistics, games theory, etc. With a specially developed software product, we generate the Melnikov equation M(t)=0 and examine all its zeros. This opens up an opportunity for the researcher to correctly understand and formulate the classical Melnikov criterion for the possible occurrence of chaos in the dynamical system. Several simulations are composed. We also demonstrate some specialized modules for investigating the dynamics of the proposed model. We further develop our model using the exponential form of the sine function. Thus, the perturbation can be interpreted as a term dependent on the characteristic function of a probability distribution. Although the original formulation leads to a distribution stated on a discrete domain, we can easily generalize the results for arbitrary distributions. Some particular examples are provided.


  • Open Access

    One More Thing on the Subject: Prediction of Chaos in a Josephson Junction with Quadratic Damping by the Melnikov Technique, Possible Probabilistic Control over Oscillations

    by Nikolay Kyurkchiev, Tsvetelin Zaevski, Anton Iliev, Vesselin Kyurkchiev, Asen Rahnev

    Many authors analyze the prediction of chaos in a Josephson junction with quadratic damping by the Melnikov technique. Due to the lack of an explicit presentation of the Melnikov integral, the researchers apply numerical methods and illustrative examples to verify a good agreement between the numerical method and the analytical one. The reader has difficulty navigating and touching upon Melnikov’s elegant theory and, in particular, the formulation of the Melnikov criterion for the possible occurrence of chaos in a dynamical system, based solely on the provided illustrations of dependencies between the main parameters of the model under consideration. The statements in a number of publications devoted to this interesting topic, such as “It is easy to see that Melnikov’s integrals are finite and not zero. It is possible to see that the transverse zeros of the Melnikov function”, do not shed enough light on the origin of the “horseshoe”-type chaos. In this paper we will try to shed additional light on this important problem. A new planar system corresponding to the N-generalized Josephson junction with quadratic damping with many free parameters is considered, which may be of interest to specialists in the field of engineering sciences. Prediction of chaos in the proposed model by the Melnikov technique is closely related to the problem of approximately simultaneously finding all roots (simple or multiple) of generalized trigonometric polynomials. Several simulations are composed. We also demonstrate some specialized modules for investigating the dynamics of the model. One application about generating stochastic construction for possible control over oscillations is also discussed.


  • Open Access

    Investigations on the Chaos in the Generalized Double Sine-Gordon Planar System: Melnikov’s Approach and Applications to Generating Antenna Factors

    by Nikolay Kyurkchiev, Tsvetelin Zaevski, Anton Iliev

    Many authors analyze the chaotic motion of the driven and damped double sine-Gordon equations and compute the Melnikov functions by numerical methods, taking an example to verify good agreement between numerical methods and analytical ones. Unfortunately, due to the lack of an explicit presentation of the Melnikov integral, the reader has difficulty navigating and touching upon Melnikov’s elegant theory and, in particular, the formulation of the Melnikov criterion for the occurrence of chaos in a dynamical system, based solely on the provided illustrations of dependencies between the main parameters of the model under consideration. In this paper we will try to shed additional light on this important problem. A new planar system corresponding to the generalized double sine-Gordon model with many free parameters is considered. We also look at the modeling of radiation diagrams and antenna factors as potential uses for the Melnikov functions. A number of simulations are created. We also show off a few specific modules for examining the model’s behavior. There is also discussion of one use for potential oscillation control.


  • Open Access

    On the impact of the penalty on the cancellable American options

    by Tsvetelin Zaevski

    The cancellable American options, also known as game options, are financial instruments that give a canceling right to the option’s writer in addition to the existing such holder’s right. The writer owes some penalty above the usual option payoff for using this right. We assume that this penalty consists of three parts – a proportion of the usual payoff, some number of shares of the underlying asset, and a fixed amount. It turns out that a cancellable option can be of one of the following three types – a regular American option, an American-style derivative that expires either at the maturity or when the underlying asset reaches the strike, or a real cancellable option. In this paper, the impact of the penalty on the option’s type is investigated. The perpetual case is only explored having in mind that it determines the kind of the finite maturity instruments in some sense.