An Improved Hybrid Algorithm to Bisection Method and Newton-Raphson Method

Transcription

1 Applied Mathematical Sciences, Vol. 11, 2017, no. 56, HIKARI Ltd, An Improved Hybrid Algorithm to Bisection Method and Newton-Raphson Method Jeongwon Kim, Taehoon Noh, Wonjun Oh, Seung Park Incheon Academy of Science and Arts Incheon 22009, Korea Nahmwoo Hahm 1 Department of Mathematics, Incheon National University Incheon 22012, Korea Copyright c 2017 Jeongwon Kim, Taehoon Noh, Wonjun Oh, Seung Park and Nahmwoo Hahm. This article is distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract In this paper, we investigate the hybrid algorithm to the bisection method and the Newton-Raphson method suggested in [1]. We suggest an improved hybrid algorithm that is suitable for functions which are not applicable to the hybrid algorithm[1]. We give some numerical results to justify our algorithm. Mathematics Subject Classification: 65H04, 65H99 Keywords: Hybrid Algorithm, Bisection Method, Newton-Raphson Method 1 Introduction Finding an approximated solution to the root of a nonlinear equation is one of the main topics of numerical analysis([4], [6]). An algorithm for finding x such that f(x) = 0 is called a root-finding algorithm. The bisection method 1 Corresponding author This research was supported by Incheon Academy of Science and Arts Fund, 2017.

2 2790 J. Kim, T. Noh, W. Oh, S. Park and N. Hahm using the intermediate value theorem is the simplest root-finding algorithm. Note that the bisection method converges slowly but it is reliable. Tanakan[7] suggested a modified bisection method using the concept of the secant method. On the other hand, the Newton-Raphson method using the derivative of a given nonlinear function is a root-finding algorithm which is more efficient than the bisection method. Note that the Newton-Raphson method converges quadratically although the bisection method converges linearly. Homeier[2] suggested a modified Newton-Raphson method with cubic convergence. Since the Newton-Raphson method may not be reliable, Altaee, Hoomod and Hussein[1] suggested a hybrid algorithm to the bisection method and the Newton-Raphson method. In addition, Hussein, Altaee and Hoomod[3] investigated a parallel hybrid algorithm to improve the simultaneous root-find algorithm suggested in [5]. In this paper, we give some examples which show that the hybrid algorithm suggested in [1] may not be complete. So, we suggested an improved hybrid algorithm that is more reliable than the hybrid algorithm[1] and more efficient than the bisection method. 2 Main Results The Hybrid algorithm suggested by Altaee, Hoomod and Hussein[1] was given as follows. Hybrid Algorithm : Given f(x), f (x), [a, b](interval) and δ = (tolerance error) Step 1 : for i = 1 to 2 Step 2 : x i = a+b 2 Step 3 : If f(x i ) = 0 or f(x i ) < δ, then go to Step 10. Step 4 : If f(a) f(x i ) < 0, then b = x i. Step 5 : Else, a = x i. Step 6 : end for Step 7 : x = x i [f(x i )/f (x i )] Step 8 : If f(x) < δ, then go to Step 10. Step 9 : x i = x and go to Step 7. Step 10 : Stop iteration.

3 Improved hybrid algorithm 2791 Hybrid Method n x n f(x n ) Table 1: Hybrid Method for f(x) = T an 1 x on [ 4, 5] In this algorithm, Altaee, Hoomod and Hussein suggested two bisection steps at the beginning and then applied the Newton-Raphson steps without considering a given function and an interval. Now, we show that the hybrid algorithm[1] may not be a good root-finding algorithm for f(x) = T an 1 x on [ 4, 5]. We obtain numerical results implemented by MATHEMATICA. As we can see in Table 1, the sequence {x n } obtained by the hybrid algorithm[1] diverges although the root of the nonlinear equation f(x) = 0 is x = 0. The main reason of this result comes from the fact that the sequence obtained by the Newton-Raphson method in the hybrid algorithm[1] may not converge although the interval containing a root of nonlinear equation reduced by applying the bisection method twice. In order to avoid the shortcoming of the hybrid algorithm[1], we suggest an improved hybrid algorithm. In our improved hybrid algorithm, we compute the x-intercept x using the Newton-Raphson method at the midpoint of the previous interval. We set [a 0, b 0 ] = [a, b]. If x [a n 1, b n 1 ], then we set x n = x and test the intermediate value theorem on [a n 1, x n ] and [x n, b n 1 ]. When we determine the interval which contains a root by the intermediate value theorem, we denote it by [a n, b n ]. If x / [a n 1, b n 1 ], then we set x n = a n 1 +b n 1 2 and test the intermediate value theorem on [a n 1, x n ] and [x n, b n 1 ]. When we determine the interval which contains a root by the intermediate value theorem, we denote it by [a n, b n ]. This process gives us a reliability for the convergence of our algorithm. In addition, our algorithm is more efficient than the bisection method since we mix the bisection method with the Newton- Raphson method.

4 2792 J. Kim, T. Noh, W. Oh, S. Park and N. Hahm Improved Hybrid Method n x n f(x n ) Table 2: Improved Hybrid Method for f(x) = T an 1 x on [ 4, 5] An Improved hybrid algorithm to the bisection method and the Newton- Raphson method is given as follows. Improved Hybrid Algorithm : Given f(x), f (x), [a, b](interval) and δ = (tolerance error) Step 1 : i = 1. Step 2 : c = a+b 2. Step 3 : if a < c f(c) f (c) < b, then x i = c f(c) f (c). Step 4 : Else, x i = a+b 2. Step 5 : If f(x i ) < δ, then go to Step 8. Step 6 : If f(a)f(x i ) < 0, then b = x i and go to Step 2. Step 7 : Else, a = x i and go to Step 2. Step 8 : Stop iteration. As we can see in Table 2, the sequence {x n } obtained by the improved hybrid algorithm converges although the sequence {x n } obtained by the hybrid algorithm[1]. In addition, the number of iteration by the improved hybrid algorithm is 13 although the number of iteration by the bisection method is 22 when the tolerance error is

5 Improved hybrid algorithm Numerical Results We suggest another example to show that the improved hybrid algorithm is more reliable than the hybrid algorithm[1]. Note that g(x) = 0 has a root on [ 5, 6] since g is continuous on [ 5, 6] and g( 5)g(6) < 0. Using MATHEMATICA, we obtain sequences by the hybrid algorithm[1] and the improved hybrid algorithm for g(x) = e sin x2 3x 5x 150 on [ 5, 6]. We use as the tolerance error. As we can see in Table 3, the sequence {x n } obtained by the improved hybrid algorithm converges although the sequence {x n } obtained by the hybrid algorithm[1] diverges. In order to show that our improved hybrid algorithm is faster than the bisection method, we select f 1 (x) = e x +cos x on [ 2, 2] and f 2 (x) = 10xe x2 1 on [ 1, 1] which are used in [7]. We use as the tolerance error. The results are given as follows. 4 Conclusion and Remarks We suggest an improved hybrid algorithm which converges to the root of a nonlinear equation faster than the bisection method. Because of the complexity of our algorithm, we don t get the rate of convergence of our improved hybrid algorithm. So, we will try to compute the rate of convergence of our improved algorithm in the future. In addition, we show by some examples that our algorithm is more reliable than the hybrid algorithm[1]. In order to get a reliable simultaneous roots of nonlinear equations, we will investigate the possibility of application of our improved hybrid algorithm to the parallel hybrid algorithm[3] in the future.

6 2794 J. Kim, T. Noh, W. Oh, S. Park and N. Hahm Hybrid Method Improved Hybrid Method n x n g(x n ) x n g(x n ) Table 3: Hybrid and Improved Hybrid Method for g(x) = e sin x2 3x 5x 150

7 Improved hybrid algorithm 2795 The Bisection Method Improved Hybrid Method n x n f 1 (x n ) x n f 1 (x n ) Table 4: Bisection and Improved Hybrid Method for f 1 (x) = e x + cos x

8 2796 J. Kim, T. Noh, W. Oh, S. Park and N. Hahm The Bisection Method Improved Hybrid Method n x n f 2 (x n ) x n f 2 (x n ) Table 5: Bisection and Improved Hybrid Method for f 2 (x) = 10xe x2 1

9 Improved hybrid algorithm 2797 References [1] Abed Ali H. Altaee, Haider K. Hoomod and Khalid Ali Hussein, A New Approach to Find Roots of Nonlinear Equations by Hybrid Algorithm to Bisection and Newton-Raphson Algorithms, Iraqi Journal for Information Technology, 7 (2015), no. 1, [2] H. H. H. Homeier, A Modified Newton Method for Rootfinding with Cubic Convergence, Journal of Computational and Applied Mathematics, 157 (2003), [3] Khalid Ali Hussein, Abed Ali H. Altaee and Haider K. Hoomod, Parallel Hybrid Algorithm of Bisection and Newton-Raphson Methods to Find Nonlinear Equations Roots, IOSR Journal of Mathematics, 11 (2015), no. 4, [4] D. Kincaid and W. Cheney, Numerical Analysis, Brooks/Cole, [5] A. J. Maeder and S. A. Wynton, Some Parallel Methods for Polynomial Root-Finding, Journal of Computational and Applied Mathematics, 18 (1987), [6] G. Miller, Numerical Analysis for Engineers and Scientists, Cambridge, [7] S. Tanakan, A New Algorithm of Modified Bisection Method for Nonlinear Equation, Applied Mathematical Sciences, 7 (2013), no. 123, Received: October 25, 2017; Published: November 9, 2017