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Fuzzy control systems have had various applications in a wide range of science and engineering in recent years. Since an unstable control system is typically useless and potentially dangerous, stability is the most important requirement for any control system (including fuzzy control system). Conceptually, there are two types of stability for control systems: Lyapunov stability (a special case of which is exponential stability) and input-output stability. This paper develops fuzzy Lyapunov stability through investigating the concept of stability for finite-dimensional systems under uncertainty and provides some related theorems. Considering the capability of fuzzy differential systems for modeling uncertainty and processing vague or subjective information in mathematical models, exponential stability and Lyapunov stability of fuzzy differential systems are presented. Also, numerical examples are given to support the theoretical results. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a new method for approximating solutions of fully fuzzy linear systems in the dual form. For this purpose, we solve the original problem in the 1-cut position (we assumed that the 1-cut is a crisp linear system), then some unknown symmetric spreads are allocated to each row of the crisp system, which leads to convert the original problem to 2 * n linear equations in order to find the symmetric spreads. Consequently, we suggested some extensions of the united solution set, the tolerable solution set and the controllable solution set. Simultaneously, we clarify between the classic hull solution sets and the extended hull solution sets in which finally leads to characterize the inner and outer estimations. Then, a financial example is solved to show the ability of proposed method. [ABSTRACT FROM AUTHOR]

Abstract: In this note we show that the example presented in a recent paper by Ghazanfari et al. is incorrect. Namely, the “exact solution” suggested by the authors is not solution of the given fuzzy differential equation (FDE). Indeed, the authors have proposed an exact solution which is independent from the initial condition. So, we obtain the correct exact solution using the characterization theorem proposed by Bede et al. under Seikkala differentiability. Also, some details are given for the mentioned example. [Copyright &y& Elsevier]

In this paper, we study existence and uniqueness of solutions of second-order fuzzy integro-differential equations with fuzzy kernel under strongly generalized differentiability. To this end, four cases are considered to show the existence of the fuzzy solution mentioned equation. Some theorems are proved, and the uniqueness of the fuzzy solution is discussed step by step. Finally, the illustrated examples are solved to investigate the conditions of theorems. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the solutions of fuzzy Volterra integral equations with separable kernel by using fuzzy differential transform method (FDTM). If the equation considered has a solution in terms of the series expansion of known functions, this powerful method catches the exact solution. To this end, we have obtained several new results to solve mentioned problem when FDTM has been applied. In order to show this capability and robustness, some fuzzy Volterra integral equations are solved in detail as numerical examples. [Copyright &y& Elsevier]

We propose a method to approximate the solutions of fully fuzzy linear system (FFLS), the so-called general solutions. So, we firstly solve the 1-cut position of a system, then some unknown spreads are allocated to each row of an FFLS. Using this methodology, we obtain some general solutions which are placed in the well-known solution sets like Tolerable solution set (TSS) and Controllable solution set (CSS). Finally, we solved two examples in order to demonstrate the ability of the proposed method. [ABSTRACT FROM AUTHOR]

A natural way to model dynamic systems under uncertainty is to use fuzzy initial value problems (FIVPs) and related uncertain systems. In this paper, we express the fuzzy Laplace transform and then some of its well-known properties are investigated. In addition, an existence theorem is given for fuzzy-valued function which possess the fuzzy Laplace transform. Consequently, we investigate the solutions of FIVPs and the solutions in state-space description of fuzzy linear continuous-time systems under generalized H-differentiability as two new applications of fuzzy Laplace transforms. Finally, some examples are given to show the efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we first propose the right and the left fuzzy Riemann–Liouville integrals; then the related left and right fuzzy Caputo differentiabilities are introduced. Consequently, some useful results about integration and differentiation of fractional order under uncertainty have been obtained. Moreover, some equivalent integral forms of original fuzzy fractional differential equations are derived. Finally, the fuzzy Ostrowski inequality about fractional case has been stated. [Copyright &y& Elsevier]

Abstract: In this paper, we propose a simple and practical method to solve a fuzzy linear system , where and are fuzzy triangular vectors with non-zero spreads and matrix is nonsingular with real coefficients. The aim of this paper is twofold. First, we obtain the crisp solution of a fuzzy linear system. To this end, we solve the 1-cut of a fuzzy linear system. Second, we allocate some unknown symmetric spreads to any rows of fuzzy linear system in 1-cut position. Thus, a fuzzy linear system in 1-cut will be transformed to a system of interval equations. The symmetric spreads of each element of a fuzzy vector solution are derived by solving such an interval system. Moreover, based on the obtained symmetric spreads we derive three types of solutions. However, one of the mentioned spreads has pessimistic/optimistic attitude that is determined with a decision maker. It seems that such a solution is a connection solution between Tolerable Solution Set (TSS) and Controllable Solution Set (CSS). Also, we derive the maximal solution and the minimal solution of an original fuzzy linear system which are placed in TSS and CSS, respectively. Finally, some numerical examples are given to illustrate the efficiency and ability of the proposed method. [Copyright &y& Elsevier]

Abstract: In this paper, we shall propose a new method to obtain symmetric solutions of a fully fuzzy linear system (FFLS) based on a 1-cut expansion. To this end, we solve the 1-cut of a FFLS (in the present paper, we assumed that the 1-cut of a FFLS is a crisp linear system or equivalently, the matrix coefficient and right hand side have triangular shapes), then some unknown symmetric spreads are allocated to each row of a 1-cut of a FFLS. So, after some manipulations, the original FFLS is transformed to solving linear equations to find the symmetric spreads. However, our method always give us a fuzzy number vector solution. Moreover, using the proposed method leads to determining the maximal- and minimal symmetric solutions of the FFLS which are placed in a Tolerable Solution Set and a Controllable Solution Set, respectively. However, the obtained solutions could be interpreted as bounded symmetric solutions of the FFLS which are useful for a large number of multiplications existing between two fuzzy numbers. Finally, some numerical examples are given to illustrate the ability of the proposed method. [Copyright &y& Elsevier]

Abstract: Linear systems have important applications in many branches of science and engineering in many applications, at least some of the parameters of the system are represented by fuzzy rather than crisp numbers. So, it is immensely important to develop a numerical procedure that would appropriately treat general fuzzy linear systems and solve them. In this paper, we propose bounded and symmetric solutions of fully fuzzy linear systems in the dual form (DFFLS) based on a 1-cut expansion. To this end, we solve the 1-cut of a DFFLS (we assumed that the 1-cut of a DFFLS is a crisp linear system), then some unknown symmetric spreads are allocated to each row of a 1-cut of a DFFLS. So, after some manipulations, the original DFFLS is transformed to solving 2∗ n linear equations to find the symmetric spreads. However, our method always give us a fuzzy vector solution. Moreover, we show that the bounded and symmetric solution of the DFFLS will be placed in the tolerable solution set (TSS) and in the controllable solution set (CSS), respectively. Also, an economic example is solved to illustrate the ability of proposed method and a new pattern is suggested for comparing the obtained solutions. [Copyright &y& Elsevier]

In this paper, a novel coronavirus infection system with a fuzzy fractional differential equation defined in Caputo's sense is developed. By using the fuzzy Laplace method coupled with Adomian decomposition transform, numerical results are obtained for better understanding of the dynamical structures of the physical behavior of COVID-19. Such behavior on the general properties of RNA in COVID-19 is also investigated for the governing model. The results demonstrate the efficiency of the proposed approach to address the uncertainty condition in the pandemic situation. [ABSTRACT FROM AUTHOR]

In [1], the authors claimed by a counterexample that the cross product definition in [2] is not correct and thus the proposed technique is false. In this note, we show that this assertion is incorrect. [ABSTRACT FROM AUTHOR]