A two-step explicit P-stable method for solving second order initial value problems

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Abstract

The conceptions of periodicity interval and P-stability were introduced by Lambert and Watson [J. Inst. Math. Appl. 18 (1976) 189] in connection with multistep methods for second order initial value problems. This paper presents a new two-step explicit P-stable method of order two for solving initial value problems of second order ordinary differential equations. Based on a special vector operation, the method can be extended to be vector applicable.

Introduction

Let us consider the initial value problem of the second order ordinary differential equationsy″=f(x,y),y(x0)=y0,y′(x0)=y′,where presume f(x,y) is sufficiently differentiable and the first derivative does not appear explicitly in f(x,y). The numerical methods have been paid much attention to in recent years because the problems are usually encountered in celestial mechanics, quantum mechanical scattering theory, theoretical physics and chemistry, and electronics. Generally, the solution of (1) is periodic, so it is expected that the result produced by some numerical method be of the analogical periodicity of the analytic solution. In 1976, Lambert and Watson [1] proposed the conceptions of periodicity interval and P-stability which can be used to discuss the stability of the numerical method for second order initial value problems. Although many P-stable methods have been proposed, such as linear multistep methods, high order hybrid P-stable methods, implicit Runge–Kutta–Nystrom and so on [2], [3], [4], [5], [6], these methods are implicit so there is an iteration subprocess needed in each step. Recently, some authors presented a class of one-step explicit A-stable methods of high order for stiff problems (see [7], [8], [9]), and with the aid of a vector operation, these methods can be extended to be vector applicable [10]. Motivated by the idea, we will present a new two-step explicit method of order two for solving (1). Based on the aforementioned special vector operation, our method can be extended to be vector applicable directly.

Section snippets

Preliminaries

To investigate the stability properties of methods for solving the initial value problem (1), Lambert and Watson [1] introduced the scalar test equationy″=−ω2y,ω∈R,When applying a symmetric two-step method to the test equation (2), one obtains the following difference equation of the form:yn+1−2C(H)yn+yn−1=0,where H=ωh,h is a fixed step length, C(H) is a rational polynomial with respect to H. The characteristic equation and polynomial are defined by the following respectively:ξ2−2C(H)ξ+1=0,

New two-step explicit P-stable method

First of all, our analysis is restricted in one-dimension space. Consider the following formula for solving the initial value problem (1):yn+1+yn−1=2ynexph2fn2yn,where h is the step length and presume yn≠0.

Applying (8) to the scalar test equation (2), one gets its characteristic equationξ2−2e−(H2/2)ξ+1=0,where H2=(ωh)2. Obviously for all H2∈(0,+∞), e−(H2/2)<1, thus method (8), as a symmetric method, is P-stable.

Let y(x) be the true solution of (1) and presume yn, yn−1 are precise. Consider the

The vector form of the method

Definition 4.1

[8]. Let a,b,dCm, d≠0, the vector product and quotient, a special vector trinary operation, of a,b,d is defined by the following:a∗bd=b∗ad:=bRe(a,d)+aRe(b,d)−dRe(b,a)(d,d),where (·,·) is the inner product in Cm,Re(·) is the real part of complex number. Define the power of the operation byd∗adn:=nd∗adad∗⋯∗adand define the exponent of the operation byd∗e(a/d):=∑+∞k=01k!d∗adk.Obviously, , is well-defined. And if a,b,c,dCm, d≠0, then(k1a+k2b)∗ck3d=k1k3a∗cd+k2k3b∗cd,k1,k2,k3∈R,k3≠0andd∗ad=a,d∗ad

Numerical results

Problem 1

Consider the scalar test equation y″=−ω2y, y(0)=1, y′(0)=0. The true solution is y(x)=cos(ωx). Set ω=10. In the numerical experiment, we take the step length h=π/200,π/400,π/800,π/1600, and for simplicity, the true value at x=h is taken as the second started value. The following table gives the errors at point x=5π, 10π, 15π, 20π.

Pointh=π200h=π400h=π800h=π1600
x=5π5.1541e0023.2539e0032.0362e0041.2731e005
x=10π2.0104e0011.3001e0028.1460e0045.0928e005
x=15π4.3307e0012.9177e002

Remark

The numerical results illustrate our method is efficient. Since it is explicit, the computational effort at each step is small relatively. However, the order of the method is low, so it needs to go on discussing how to improve its accuracy so as to adapt the big step length.

References (11)

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