Dulranga's Notes
Semester 3MathematicsDifferential EquationsLaplace Transform

Inverse Laplace transform

This is the transformation we do to get back into the continuous time domain from the complex frequency domain.

L{f(t)}=F(s)  ⟹  L−1{F(s)}=f(t)\mathcal{L}\{f(t)\} = F(s) \implies \mathcal{L}^{-1}\{F(s)\} = f(t)

The Formal Definition

Formally, the inverse Laplace transform is defined as a complex contour integral known as the Bromwich integral:

f(t)=12πj∫γ−j∞γ+j∞F(s)est dsf(t) = \frac{1}{2\pi j} \int_{\gamma - j\infty}^{\gamma + j\infty} F(s) e^{st} \, ds

here, s=γ+jωs = \gamma + j\omega and ω\omega ranges from −∞-\infty to +∞+\infty γ\gamma is a chosen real number that is entirely within the ROC of F(s)F(s)

inverse laplace transform line.png inverse laplace transform.png

Practical Solving problems

in practical, never really requires the formal definition to solve inverse laplace transforms. You can use partial fraction decomposition and Laplace Transform Table

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