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[parent] using Laplace transform to solve initial value problems (Example)

Since the Laplace transforms of the derivatives of $f(t)$ are polynomials in the transform parameter $s$ (see table of Laplace transforms), forming the Laplace transform of a linear differential equation with constant coefficients and initial conditions at $t = 0$ yields generally a simple equation 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 $$f''(t)+2f'(t)+f(t) = e^{-t} \quad (f(0) = 0,\;\; f'(0) = 1)$$ gives $$[s^2F(s)-sf(0)-f'(0)]+2[sF(s)-f(0)]+F(s) = \frac{1}{s+1},$$ i.e. $$(s^2+2s+1)F(s) = 1+\frac{1}{s+1},$$ whence $$F(s) = \frac{1}{(s+1)^2}+\frac{1}{(s+1)^3}.$$ Taking the inverse Laplace transform produces the result $$f(t) \,=\, te^{-t}+\frac{t^2e^{-t}}{2} \;=\; \frac{e^{-t}}{2}(t^2+2t).$$




"using Laplace transform to solve initial value problems" is owned by pahio.
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See Also: table of Laplace transforms, Laplace transform


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Cross-references: inverse, differential equation, general solution, function, equation, simple, initial conditions, coefficients, linear differential equation, table of Laplace transforms, transform parameter, polynomials, derivatives, Laplace transforms

This is version 6 of using Laplace transform to solve initial value problems, born on 2008-08-06, modified 2008-08-15.
Object id is 10922, canonical name is UsingLaplaceTransformToInitialValueProblems.
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AMS MSC34A12 (Ordinary differential equations :: General theory :: Initial value problems, existence, uniqueness, continuous dependence and continuation of solutions)
 44A10 (Integral transforms, operational calculus :: Laplace transform)

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to or for? by pahio on 2008-08-07 10:44:47
Is "to" the right preposition in the title of http://planetmath.org/encyclopedia/UsingLaplaceTransformToInitialValueProblems.html ?
Maybe "for" were better?
Jussi
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