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单词 LaplaceTransformOfLogarithm
释义

Laplace transform of logarithm


Theorem.  The Laplace transformDlmfMathworldPlanetmath of the natural logarithmMathworldPlanetmathPlanetmathPlanetmath functionMathworldPlanetmath is

{lnt}=Γ(1)-lnss

where Γ is Euler’s gamma functionDlmfDlmfMathworldPlanetmath.

Proof.  We use the Laplace transform of the power functionDlmfDlmfPlanetmath (http://planetmath.org/LaplaceTransformOfPowerFunction)

0e-stta𝑑t=Γ(a+1)sa+1

by differentiating it with respect to the parametre a:

0e-sttalntdt=Γ(a+1)sa+1-Γ(a+1)sa+1lns(sa+1)2=Γ(a+1)-Γ(a+1)lnssa+1

Setting here  a=0,  we obtain

{lnt}=0e-stlntdt=Γ(1)-1lnss,

Q.E.D.

Note.  The number Γ(1) is equal the of the Euler–Mascheroni constant (http://planetmath.org/EulersConstant), as is seen in the entry digamma and polygamma functions.

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更新时间:2025/5/4 16:54:33