Monday, September 1, 2008

Analytical Solution Of The Ricatti Differential Equation For High Frequency Derived By Using The Stable Modulation Technique

The Ricatti differential equation dy/dt = P(t)y2+Q(t)y+R(t) is a nonlinear differential equation which is of contemporary interest in various fields, including particle dynamics, optics, and petroleum exploration. The Ricatti differential equation is easily solved by numerical methods. But in order to obtain the exact solution in analytical form, the first order of nonlinear inhomogeneous differential equation is commonly convert into a second order linear differential equation by use of a change of the dependent variable. In this paper we introduce the stable modulation technique (SMT) to solve the Ricatti differential equation without of the use linearization procedure. The main principle of the SMT in solving a first order nonlinear differential equation is modulate the solution of the linear part into the initial value of the nonlinear part solution. Important to be stressed here that the solution of nonlinear part must be written in the modulation function, where the initial value acts as amplitude and also including in the total phase shift. For a special case, dy/dt = -by2+ay+Acos(2πft) where a and b of both are constants, while t is variable of the time (in s), frequency f in Herzt (Hz) we find that the analytical solution of the SMT is appropriate with numerical solution espescially for high frequency f≥10 Hz, amplitude value A≤1, and initial value of the y in the range 0.1≤y0≤1. The analytical solution above can be used as trial function when the Ricatti differential equation will be solved by using combination of the modulational instability technique and variational approximation.

Keywords : Nonlinear inhomogeneous differential equation, linearization procedure, stable modulation technique, modulational instability

I. Introduction

The general form of the Ricatti differential equation (DE) is of the form :
dy/dt = P(t)y2+Q(t)y+R(t), .......................................(1)
where y and t are respectively dependent and independent variables, both of P(t) and Q(t) are homogeneous coefficients, where R(t) is the inhomogeneous term[1]. The Ricatti DE is mother of all ordinary differential equations (ODE’s) second order generating special functions like Airy, Bessel and etc,[2] even the Helmholtz equation[3] which has broad applications including optics and geophysics. Common procedure in solving the Ricatti DE is by transforming into a linear ODE second order[1],[2],[4]. For special case, the analytical exact solution of the Ricatti DE can not be obtained, because the analytical solution of the corresponding linear ODE second order is not available.

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