# Publications by Year: 2020

2020
Mosić, D., Stanimirović, P. S., Sahoo, J. K., Behera, R., & Katsikis, V. N. (2020). One-sided weighted outer inverses of tensors. Journal of Computational and Applied Mathematics. presented at the 2020. Publisher's VersionAbstract
In this paper, for the first time in literature, we introduce one-sided weighted inverses and extend the notions of one-sided inverses, outer inverses and inverses along given elements. Although our results are new and in the matrix case, we decided to present them in tensor space with reshape operator. For this purpose, a left and right (M,N)-weighted (B,C)-inverse and the (M,N)-weighted (B,C)-inverse of a tensor are defined. Additionally, necessary and sufficient conditions for the existence of these new inverses are presented. We describe the sets of all left (or right) (M,N)-weighted (B,C)-inverses of a given tensor. As consequences of these results, we consider the one-sided (B,C)-inverse, (B,C)-inverse, one-sided inverse along a tensor and inverse along a tensor. Further, we introduce a (M,N)-weighted (B,C)-outer inverse and a W-weighted (B,C)-outer inverse of tensors with a few characterizations. Then, corresponding algorithms for computing various types of outer inverses of tensors are proposed, implemented and tested. The prowess of the proposed inverses are demonstrated for finding the solution of Poisson problem and the restoration of 3D color images.
Medvedeva, M., Simos, T. E., Tsitouras, C., & Katsikis, V. (2020). Direct estimation of SIR model parameters through second-order finite differences. Mathematical Methods in the Applied Sciences, n/a(n/a). presented at the 2020, John Wiley & Sons, Ltd. Publisher's VersionAbstract
SIR model is widely used for modeling the infectious diseases. This is a system of ordinary differential equations (ODEs). The numbers of susceptible, infectious, or immunized individuals are the compartments in these equations and change in time. Two parameters are the factor of differentiating these models. Here, we are not interested in solving the ODEs describing a certain SIR model. Given the observed data, we try to estimate the parameters that determine the model. For this, we propose a least squares approach using second-order centered differences for replacing the derivatives appeared in the ODEs. Then we arrive at a simple linear system that can be solved explicitly and furnish the approximations of the parameters. Numerical results over various artificial data verify the simplicity and accuracy of the new method.
Mosić, D., Stanimirović, P. S., & Katsikis, V. N. (2020). Solvability of some constrained matrix approximation problems using core-EP inverses. Computational and Applied Mathematics, 39(4), 311. presented at the 2020. Publisher's VersionAbstract
Using the core-EP inverse, we obtain the unique solution to the constrained matrix minimization problem in the Euclidean norm: $$\mathrm{Minimize }\ \Vert Mx-b\Vert _2$$Minimize‖Mx-b‖2, subject to the constraint $$x\in \mathcal{R}(M^k),$$x∈R(Mk),where $$M\in {\mathbb {C}}^{n\times n}$$M∈Cn×n, $$k=\mathrm {Ind}(M)$$k=Ind(M)and $$b\in {\mathbb {C}}^n$$b∈Cn. This problem reduces to well-known results for complex matrices of index one and for nonsingular complex matrices. We present two kinds of Cramer’s rules for finding unique solution to the above mentioned problem, applying one well-known expression and one new expression for core-EP inverse. Also, we consider a corresponding constrained matrix approximation problem and its Cramer’s rules based on the W-weighted core-EP inverse. Numerical comparison with classical strategies for solving the least squares problems with linear equality constraints is presented. Particular cases of the considered constrained optimization problem are considered as well as application in solving constrained matrix equations.
Stanimirović, P. S., Katsikis, V. N., & Gerontitis, D. (2020). A New Varying-Parameter Design Formula for Solving Time-Varying Problems. Neural Processing Letters. presented at the 2020. Publisher's VersionAbstract
A novel finite-time convergent zeroing neural network (ZNN) based on varying gain parameter for solving time-varying (TV) problems is presented. The model is based on the improvement and generalization of the finite-time ZNN (FTZNN) dynamics by means of the varying-parameter ZNN (VPZNN) dynamics, and termed as VPFTZNN. More precisely, the proposed model replaces fixed and large values of the scaling parameter by an appropriate time-dependent gain parameter, which leads to a faster and bounded convergence of the error function in comparison to previous ZNN methods. The convergence properties of the proposed VPFTZNN dynamical evolution in its generic form is verified. Particularly, VPFTZNN for solving linear matrix equations and for computing generalized inverses are investigated theoretically and numerically. Moreover, the proposed design is applicable in solving the TV matrix inversion problem, solving the Lyapunov and Sylvester equation as well as in approximating the matrix square root. Theoretical analysis as well as simulation results validate the effectiveness of the introduced dynamical evolution. The main advantages of the proposed VPFTZNN dynamics are their generality and faster finite-time convergence with respect to FTZNN models.
Medvedeva, M.  A., Katsikis, V.  N., Mourtas, S.  D., & Simos, T. E. (2020). Randomized time-varying knapsack problems via binary beetle antennae search algorithm: Emphasis on applications in portfolio insurance. Mathematical Methods in the Applied Sciences. presented at the 2020, John Wiley & Sons, Ltd. Publisher's VersionAbstract
The knapsack problem is a problem in combinatorial optimization, and in many such problems, exhaustive search is not tractable. In this paper, we describe and analyze the randomized time-varying knapsack problem (RTVKP) as a time-varying integer linear programming (TV-ILP) problem. In this way, we present the on-line solution to the RTVKP combinatorial optimization problem and highlight the restrictions of static methods. In addition, the RTVKP is applied in the field of finance and converted into a portfolio insurance problem. Our methodology is confirmed by simulation tests in real-world data sets, in order to explain being an excellent alternative to traditional approaches.
Katsikis, V. N., & Mourtas, S. D. (2020). Optimal Portfolio Insurance under Nonlinear Transaction Costs. Journal of Modeling and Optimization, 12(2), 117-124.
Khan, A. T., Cao, X., Li, S., Hu, B., & Katsikis, V. N. (2020). Quantum Beetle Antennae Search: A Novel Technique for The Constrained Portfolio Optimization Problem. SCIENCE CHINA Information Sciences. Science China Press.
Sahoo, J. K., Behera, R., Stanimirović, P. S., & Katsikis, V. N. (2020). Computation of outer inverses of tensors using the QR decomposition. Computational and Applied Mathematics, 39, 1–20. Springer International Publishing.
Khan, A. H., Cao, X., Li, S., Katsikis, V. N., & Liao, L. (2020). BAS-ADAM: An ADAM based approach to improve the performance of beetle antennae search optimizer. IEEE/CAA Journal of Automatica Sinica, 7, 461–471. IEEE.
Gerontitis, D., Moysis, L., Stanimirović, P., Katsikis, V. N., & Volos, C. (2020). Varying-parameter finite-time zeroing neural network for solving linear algebraic systems. Electronics Letters, 56, 810–813. IET.
Katsikis, V. N., Mourtas, S. D., Stanimirović, P. S., Li, S., & Cao, X. (2020). Time-varying minimum-cost portfolio insurance under transaction costs problem via Beetle Antennae Search Algorithm (BAS). Applied Mathematics and Computation, 385, 125453. Elsevier.
Sahoo, J. K., Behera, R., Stanimirović, P. S., Katsikis, V. N., & Ma, H. (2020). Core and core-EP inverses of tensors. Computational and Applied Mathematics, 39, 9. Springer International Publishing.
Stanimirović, P. S., Ćirić, M., Katsikis, V. N., Li, C., & Ma, H. (2020). Outer and (b, c) inverses of tensors. Linear and Multilinear Algebra, 68, 940–971. Taylor & Francis.
Khan, A. H., Cao, X., Katsikis, V. N., Stanimirović, P., Brajević, I., Li, S., Kadry, S., et al. (2020). Optimal Portfolio Management for Engineering Problems Using Nonconvex Cardinality Constraint: A Computing Perspective. IEEE Access, 8, 57437–57450. IEEE.