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单词 LaplaceTransform
释义

Laplace transform


Let f(t) be a functionMathworldPlanetmath defined on the interval  [0,). TheLaplace transformDlmfMathworldPlanetmath of f(t) is the function F(s) defined by

F(s)=0e-stf(t)𝑑t,

provided that the integral converges. 11Depending on the definition ofintegral one is using, one may prefer to define the Laplace transform aslimx0+xe-stf(t)𝑑t It suffices that f be defined when t>0 and s can be complex. We willusually denote the Laplace transform of f by {f}. Someof the most common Laplace transforms are:

  1. 1.

    {eat}=1s-a,s>a

  2. 2.

    {cos(bt)}=ss2+b2,s>0

  3. 3.

    {sin(bt)}=bs2+b2,s>0

  4. 4.

    {tn}=Γ(n+1)sn+1,s>0,n>-1.

  5. 5.

    {f}=s{f}-limx0+f(x)

For more particular Laplace transforms, see the table of Laplacetransforms.

Notice the Laplace transform is a linear transformation. It is worth noting that, if

0e-st|f(t)|𝑑t<

for some  s, then {f} is an analytic function in the complex half-plane{zz>s}.

Much like the Fourier transformDlmfMathworldPlanetmath, the Laplace transform has a convolutionMathworldPlanetmath. However, the form of the convolution used is different.

{f*g}={f}{g}

where

(f*g)(t)=0tf(t-s)g(s)𝑑s

and

{fg}(s)=c-ic+i{f}(z){g}(s-z)𝑑z

The most popular usage of the Laplace transform is to solveinitial value problemsMathworldPlanetmathPlanetmath by taking the Laplace transform of bothsides of an ordinary differential equationMathworldPlanetmath; see the entry“image equation (http://planetmath.org/ImageEquation)”.

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更新时间:2025/5/4 9:17:29