The root-fnding problem of a univariate nonlinear equation is a fundamental and long-studied problem, and has wide applications in mathematics and engineering computation. In this paper, two modified Newton-type methods and two variants of Super-Halley’s method to solve nonlinear equations are brought forward. Analytical discussions are reported and the theoretical efficiency of the methods is studied. Both of Algorithms 1 and 2 require three evaluations of the functions and two evaluations of derivatives at each iteration. Therefore the efficiency indices of Algorithms 1 and 2 are 1.431 and 1.476, respectively. The presented variants of Super-Halley’s methods require two evaluations of the functions and two evaluations of derivatives at each iteration. Therefore the efficiency indices of Algorithms 3 and 4 are 1.565. Hence, all efficiency indices of the proposed algorithms are better than that of classical Newton’s method 1.414. All of the proposed algorithms in this paper are free from second derivatives. Some numerical results are finally provided to support the theoretical discussions of the proposed methods.
One of the most important questions in mathematics is how to find a solution of the nonlinear equation
where for an open interval has sufficient number of continuous derivatives in a neighborhood of . There are very few functions for which the roots can be expressed explicitly in closed form. Thus, the solutions must be obtained approximately, relying on numerical techniques based on iterative processes. Solving nonlinear equations is a classical problem which has interesting applications in various branches of science, and engineering computation. The nonlinear equations play an important role in many fields of science, and many numerical methods are developed. In this paper, we apply iterative methods to find a simple root of the above problem.
It is well known that Newton’s method (NM for simplicity) is one of the most famous and important methods for computing approximations by the following iterative scheme [5]
The Newton’s method converges quadratically in some neighborhood of for some appropriate start value . The main advantage of this method is that the computation of the second derivative not required.
An acceleration of Newton’s method, called Super-Halley method (SHM for simplicity) [39], which is defined by
where
This method is, in general, an iterative process with order of convergence three although the method converges with fourth order when it is applied to quadratic equations. From a practical point of view, it is interesting and expected to research higher-order variants of Super-Halley method for general non-linear equations.
In the past decades, much attention has been paid to develop iterative methods for solving nonlinear equations, and a large number of researchers try to improve Newton’s method in order to get a method with a higher order of convergence and more accuracy in open literatures, see for example [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39] and the references therein for more details.
Motivated and inspired by the ongoing activities in the direction, in this paper, to improve the local order of convergence properties, we present two modified Newton-type iterative methods and two variants of Super-Halley method for solving nonlinear equations. All of the proposed algorithms in this paper are free from second derivatives. At each iteration, Algorithms 1 and 2 require three evaluations of the functions and two evaluations of derivatives, and Algorithms 3 and 4 require two evaluations of the functions and two evaluations of derivatives. Some numerical results are given to illustrate the advantage and effectiveness of the methods.
The rest of the paper is organized as follows: In Section 2 we describe two new modified Newton-type iterative methods and we analyze their convergence. In Section 3, we give two variant of Super-Halley method and analyze their convergence. Different numerical tests confirm the theoretical results and allow us to compare our new methods with some other known methods in Section 4. Finally, the conclusions are given in Section 5.
Two new modified Newton-type iterative methods and analysis of their convergence
Firstly, we consider the following iterative scheme.
Algorithm 1. For given , we consider the following iteration method for solving nonlinear Eq. (1)
For Algorithm 1, we have the following convergence result.
Theorem 1. Assume that the function has a single root , where is an open interval. If has first, second and third derivatives in the interval , then Algorithm 1 defined by Eqs (4)–(6) is sixth-order convergent in a neighborhood of and it satisfies the following error equation
where
Proof. Let be the simple root of , and
Consider the iteration function defined by
where
By some computations using Maple we can obtain
Furthermore, from the Taylor expansion of at , we have
Therefore, we have the error expression of the algorithm
which means the order of convergence of Algorithm 1 is six. The proof is completed.
Now, we propose the following seventh-order convergent iterative method and give its convergence analysis.
Algorithm 2. For given , we consider the following iteration scheme
For Algorithm 2, we have the following convergence result.
Theorem 2. Assume that the function has a single root , where is an open interval. If has first, second and third derivatives in the interval , then Algorithm 2 defined by Eqs (15)–(17) is seventh-order convergent in a neighborhood of and its error equation is
which shows that the order of convergence of Algorithm 2 is seven.
Two variants of Super-Halley’s methods and their convergence analysis
In this section, we consider the following two sixth-order variants of Super-Halley’s method. Firstly, we give the following iterative scheme.
Algorithm 3. For given , we consider the following iteration method for solving nonlinear Eq. (1)
For Algorithm 3, we have the following convergence result.
Theorem 3. Assume that the function has a single root , where is an open interval. If has first, second and third derivatives in the interval , then Algorithm 3 defined by Eqs (22)–(24) is sixth-order convergent in a neighborhood of and it satisfies the following error equation
where
Proof. Let be the simple root of , and
Consider the iteration function defined by
where
By some computations using Maple we can obtain
Furthermore, from the Taylor expansion of at , we have
Therefore, we have the error expression of the algorithm
which means the order of convergence of the Algorithm 3 is six. The proof is completed.
Next, we propose the following variant of Super-Halley’s method.
Algorithm 4. For given , we consider the following iteration method for solving nonlinear Eq. (1)
For Algorithm 4, we have the following convergence result.
Theorem 4. Assume that the function has a single root , where is an open interval. If has first, second and third derivatives in the interval , then Algorithm 4 defined by Eq. (29)–(31) is sixth-order convergent in a neighborhood of and it satisfies the following error equation
where
Proof. Let be the simple root of , and
Consider the iteration function defined by
where
By some computations using Maple we can obtain
Furthermore, from the Taylor expansion of at , we have
Therefore, we have the error expression of the algorithm
which means the order of convergence of Algorithm 4 is six. The proof is completed.
As the order of an iterative method increases, so does the number of function evaluations per step. The efficiency index gives a measure of balance between those quantities, according to the formula , where is the order of the method and is the number of function evaluations per iteration required by the method. It is not hard to see that the efficiency indices of Algorithms 1 and 2 are 1.431 and 1.476, respectively, and the efficiency indices of Algorithms 3 and 4 are 1.565, which are all better than that of classical Newton’s method (NM) 1.414.
Numerical results
This section is devoted to checking the effectiveness and efficiency of our proposed methods Algorithms 1–4 with NM, SHM, and PPM method defined by
which is third-order convergent with efficiency index 1.442.
Table 1 shows the number of iterations (ITs) required to satisfy the stopping criterion. All computations were done by using MATLAB 7.0 and using 64 digit floating point arithmetics. In Table 1, we use the following functions.
Comparison of various methods
Functions
NM
PPM
SHM
Algorithm 1
Algorithm 2
Algorithm 3
Algorithm 4
1.5
5
4
4
3
3
3
3
2.0
6
5
4
4
3
4
4
2.3
5
4
4
3
4
3
3
1.6
6
5
5
4
4
4
4
1.2
5
4
4
3
3
3
3
1.4
4
3
3
3
2
3
3
0.6
4
3
3
3
3
3
3
3.1
7
3
3
3
3
3
3
7.8
12
6
5
5
3
4
4
0.7
6
4
4
3
4
4
4
2.4
6
4
3
3
3
3
3
1.4
7
56
6
5
4
4
5
0.7
6
5
4
3
3
3
3
0.75
8
6
5
4
3
4
3
2
16
11
8
6
6
5
6
1.8
12
8
6
4
4
4
4
1
11
8
5
4
3
4
4
1.2
14
6
5
4
4
4
4
1
10
5
4
3
3
3
3
0.95
15
8
5
4
4
4
4
1
16
10
7
6
4
5
5
1.5
18
11
8
6
4
5
6
0.5
8
5
4
3
3
3
3
0.8
11
7
6
5
4
5
5
The computational results in Table 1 show that Algorithms 1–4 require less ITs than NM. Therefore, the proposed four methods are of practical interest and can compete with NM and PPM.
Conclusions
This paper presented and analyzed two modified Newton-type iterative methods and two variants of Super-Halley’s method for solving nonlinear equations. The methods are free from second derivatives. Algorithms 1 and 2 require three evaluations of the functions and two evaluations of derivatives at each step. Algorithms 3 and 4 require two evaluations of the functions and two evaluations of derivatives per iteration. Several numerical tests demonstrate that the methods proposed in the paper are more efficient and perform better than Newton’s method, SHM, and PPM.
Footnotes
Acknowledgments
The authors acknowledge the Project of National Natural Science Foundation of China (11241005), Research Project Supported by Shanxi Scholarship Council of China (2015-093), Fund Program for the Scientific Activities of Selected Returned Overseas Professionals in Shanxi Province, the Fund for Shanxi Key Subjects Construction (FSKSC), Natural Science Foundation of Shandong province (Grant: ZR2016AM06), Excellent Young Scientist Foundation of Shandong Province (Grant: BS2011SF024), Yuncheng University Academic Scientific Research Project (YQ-2012020).
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