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Mathematical Methods for Physics and Engineering - Matematica.NET

Mathematical Methods for Physics and Engineering - Matematica.NET

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25.5 INVERSE LAPLACE TRANSFORMΓRΓRΓRLLL(a) (b) (c)Figure 25.7 Some contour completions <strong>for</strong> the integration path L of theinverse Laplace trans<strong>for</strong>m. For details of when each is appropriate see themain text.plausible:∫ λ+i∞f(x) = 1∫ ∞ds e sx e −su f(u) du, Re(s) > 0, i.e. λ>0,2πi λ−i∞0= 1 ∫ ∞ ∫ λ+i∞du f(u) e s(x−u) ds2πi 0λ−i∞= 1 ∫ ∞ ∫ ∞du f(u) e λ(x−u) e ip(x−u) i dp, putting s = λ + ip,2πi 0−∞= 1 ∫ ∞f(u)e λ(x−u) 2πδ(x − u) du2π 0{ f(x) x ≥ 0,=(25.26)0 x

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