2024-08

Journal of mathematics and computer science (Issue : 3) (Volume : 36)

This work introduces a new variation of the Hestenes and Stiefel nonlinear conjugate gradient (HS) method by combining the advantages of the spectral conjugate gradient method and the conjugacy condition of the quasi-Newton method. The proposed method incorporates inexact line searches and categorizing it as a descent method. By employing line searches that satisfy the Wolfe conditions, we establish sufficient descent properties and global convergence condition, assuming that the appropriate conditions are met. Additionally, we perform numerical experiments utilizing benchmark functions frequently used in optimization assignments to evaluate the effectiveness of the proposed method. The results demonstrate that our method outperforms the traditional HS method. Furthermore, we successfully implement the newly developed technique to train neural networks (NNs), demonstrating its practicality for non-traditional optimization tasks.

2023-12

Science Journal of University of Zakho (Issue : 4) (Volume : 11)

The method of optimization is used to determine the most precise value for certain functions within a certain domain; it is mostly studied and employed in the fields of mathematics, computer science, and physics. This work presents a novel three-term conjugate gradient (CG) approach for unconstrained optimization problems. Both the descending criteria and the sufficient descent criterion were met by the new approach. The novel method that has been proposed has been evaluated for global convergence. The outcomes of numerical trials on a few well-known test functions demonstrated how highly successful our new modified method is, depending on the number of iterations (NOI) and the number of functions to be evaluated (NOF).

2023-06

Mathematics and Statistics (Issue : 4) (Volume : 11)

Optimization refers to the process of finding the best possible solution to a problem within a given set of constraints. It involves maximizing or minimizing a specific objective function while adhering to specific constraints. Optimization is used in various fields, including mathematics, engineering, economics, computer science, and data science, among others. The objective function can be a simple equation, a complex algorithm, or a mathematical model that describes a system or process. There are various optimization techniques available, including linear programming, nonlinear programming, genetic algorithms, simulated annealing, and particle swarm optimization, among others. These techniques use different algorithms to search for the optimal solution to a problem. In this paper, the main goal of unconstrained optimization is to minimize an objective function that uses real variables and has no value restrictions. In this study, based on the modified conjugacy condition, we offer a new conjugate gradient (CG) approach for nonlinear unconstrained problems in optimization. The new method satisfied the descent condition and the sufficient descent condition. We compare the numerical results of the new method with the Hestenes-Stiefel (HS) method. Our novel method is quite effective according to the number of iterations (NOI) and the number of functions (NOF) evaluated, as demonstrated by the numerical results on certain well-known non-linear test functions.

2023-01

Mathematics and Statistics (Issue : 1) (Volume : 11)

The major stationary iterative method used to solve nonlinear optimization problems is the quasi-Newton (QN) method. Symmetric Rank-One (SR1) is a method in the quasi-Newton family. This algorithm converges towards the true Hessian fast and has computational advantages for sparse or partially separable problems [1]. Thus, investigating the efficiency of the SR1 algorithm is significant. It's possible that the matrix generated by SR1 update won't always be positive. The denominator may also vanish or become zero. To overcome the drawbacks of the SR1 method, resulting in better performance than the standard SR1 method, in this work, we derive a new vector 𝑦𝑦𝑘𝑘 ∗ depending on the Barzilai-Borwein step size to obtain a new SR1 method. Then using this updating formula with preconditioning conjugate gradient (PCG) method is presented. With the aid of inexact line search procedure by strong Wolfe conditions, the new SR1 method is proposed and its performance is evaluated in comparison to the conventional SR1 method. It is proven that the updated matrix of the new SR1 method, 𝐻𝐻𝑘𝑘+1 𝑛𝑛𝑛𝑛𝑛𝑛, is symmetric matrix and positive definite matrix, given 𝐻𝐻𝑘𝑘 is initialized to identity matrix. In this study, the proposed method solved 13 problems effectively in terms of the number of iterations (NI) and the number of function evaluations (NF). Regarding NF, the new SR1 method also outperformed the classic SR1 method. The proposed method is shown to be more efficient in solving relatively large-scale problems (5,000 variables) compared to the original method. From the numerical results, the proposed method turned out to be significantly faster, effective and suitable for solving large dimension nonlinear equations

2022-11

Journal of Duhok University (Issue : 2) (Volume : 25)

In this paper, we propose two hybrid gradient based methods and genetic algorithm for solving systems of linear equations with fast convergence. The first proposed hybrid method is obtained by using the steepest descent method and the second one by the Cauchy-Barzilai-Borwein method. These algorithms are based on minimizing the residual of solution which has genetic characteristics. They are compared with the normal genetic algorithm and standard gradient based methods in order to show the accuracy and the convergence speed of them. Since the conjugate gradient method is recommended for solving large sparse and symmetric positive definite matrices, we also compare the numerical results of our proposed algorithms with this method. The numerical results demonstrate the robustness and efficiency of the proposed algorithms. Moreover, we observe that our hybridization of the CBB method and genetic algorithm gives more accurate results with faster convergence than other mentioned methods in all given cases

2022-08

General Letters in Mathematics (Issue : 2) (Volume : 12)

The steepest descent (SD) method is well-known as the simplest method in optimization. In this paper, we propose a new SD search direction for solving system of linear equations Ax= b. We also prove that the proposed SD method with exact line search satisfies descent condition and possesses global convergence properties. This proposed method is motivated by previous work on the SD method by Zubai’ah-Mustafa-Rivaie-Ismail (ZMRI)[2]. Numerical comparisons with a classical SD algorithm and ZMRI algorithm show that this algorithm is very effective depending on the number of iterations (NOI) and CPU time.

2021-10

Journal of Duhok University (Issue : 2) (Volume : 24)

In this paper a new conjugate gradient method for unconstrained optimization is suggested, the new method is based on Conjugate Descent (CD) formula which is a modified of the CD formula and which is also sufficiently descent and globally convergent. Numerical evidence shows that this new conjugate gradient algorithm is considered as one of the competitive conjugate gradient methods.

2016-10

University of Zakho (Issue : 1) (Volume : 4)

In this paper, we propose a modification of the self-scaling quasi-Newton (DFP) method for unconstrained optimization using logistic mapping. We shoe that it produces a positive definite matrix. Numerical results demonstrate that the new algorithm is superior to standard DFP method with respect to the NOI and NOF.

2016-07

University of Duhok (Issue : 1) (Volume : 19)

The conjugate gradient method is one of the most important algorithms for solving large and sparse symmetric positive definite (SPD) matrices. In this paper, the sufficient condition for convergence of the Fletcher-Reeves conjugate gradient method for almost symmetric matrices when the Euclidean norm of the nonsymmetric part of a positive definite matrix is less than the value of which is related to the smallest and the largest eigenvalues of the symmetric part of the matrix under consideration is presented.

2015-11

University of Zakho (Issue : 1) (Volume : 3)

Due to its simplicity and numerical efficiency, the Barzilai and Borwein (BB) gradient method has received numerous attentions in different scientific fields. In this paper, the sufficient condition for convergence of the BB method when the coefficient matrix of linear algebraic equations is slightly unsymmetric with positive definite symmetric part is presented.

2015-09

International Journal of Enhanced Research in Science Technology & Engineering (Issue : 5) (Volume : 4)

In this paper, we proposed a new conjugate gradient method for unconstrained optimization problems by using Logistics Equation, One of the remarkable properties of the conjugate gradient method is its ability to generate so they are widely used for large scale unconstrained optimization problems.

2006-05

Dohuk University (Issue : 1) (Volume : 9)

An investigation to minimization conjugate gradient type methods

2005-06

Dohuk University (Issue : 1) (Volume : 8)

A modified algorithm for the combined Barrier-Penalty constrained problem