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单词 UsingLaplaceTransformToSolveInitialValueProblems
释义

using Laplace transform to solve initial value problems


Since the Laplace transformsMathworldPlanetmath of the derivatives of f(t) arepolynomials in the transform parameter s (see table of Laplacetransforms), forming the Laplace transform of a linear differentialequation with constant coefficients and initial conditionsMathworldPlanetmath at t=0 yields generally a simple equation(image equation (http://planetmath.org/imageequation)) for solving the transformed function F(s).  Since the initial conditions can be taken into consideration instantly, one needs not to determine the general solution of the differential equation.

For example, transforming the equation

f′′(t)+2f(t)+f(t)=e-t  (f(0)=0,f(0)=1)

gives

[s2F(s)-sf(0)-f(0)]+2[sF(s)-f(0)]+F(s)=1s+1,

i.e.

(s2+2s+1)F(s)=1+1s+1,

whence

F(s)=1(s+1)2+1(s+1)3.

Taking the inverse Laplace transform produces the result

f(t)=te-t+t2e-t2=e-t2(t2+2t).
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更新时间:2025/5/4 5:54:16