Module for Convolution Method for Laplace Transforms

Numerical Methods for O. D. E.  using Mathematica. (c) John H. Mathews, 2003

Background.  (Convolution Theorem)

    Let  [Graphics:Images/LaplaceTransformConvolutionMod_gr_1.gif]  denote the Laplace transforms of  [Graphics:Images/LaplaceTransformConvolutionMod_gr_2.gif],  respectively.  Then the product [Graphics:Images/LaplaceTransformConvolutionMod_gr_3.gif]is the Laplace transform of the convolution of  [Graphics:Images/LaplaceTransformConvolutionMod_gr_4.gif],  and is denoted by  [Graphics:Images/LaplaceTransformConvolutionMod_gr_5.gif],  and has the integral representation
    
    [Graphics:Images/LaplaceTransformConvolutionMod_gr_6.gif],
    or
    [Graphics:Images/LaplaceTransformConvolutionMod_gr_7.gif].

Example 1.  Use convolution to find the inverse Laplace transform of  [Graphics:Images/LaplaceTransformConvolutionMod_gr_8.gif].  

Solution 1.

Example 2.  Use the convolution theorem to solve the integral equation  

    [Graphics:Images/LaplaceTransformConvolutionMod_gr_28.gif].  

Solution 2.

More Background.

The Laplace transform of the Dirac delta function  [Graphics:Images/LaplaceTransformConvolutionMod_gr_51.gif]  is  [Graphics:Images/LaplaceTransformConvolutionMod_gr_52.gif].  
This can be illustrated with Mathematica.

[Graphics:Images/LaplaceTransformConvolutionMod_gr_53.gif]
[Graphics:Images/LaplaceTransformConvolutionMod_gr_54.gif]
[Graphics:Images/LaplaceTransformConvolutionMod_gr_55.gif]

Example 3.  Solve the initial value problem  

[Graphics:Images/LaplaceTransformConvolutionMod_gr_56.gif]  with   [Graphics:Images/LaplaceTransformConvolutionMod_gr_57.gif].  

Solution 3.

Example 4.   Use convolution to solve the initial value problem  

[Graphics:Images/LaplaceTransformConvolutionMod_gr_76.gif]  with  [Graphics:Images/LaplaceTransformConvolutionMod_gr_77.gif].  

Plot the solution over the interval  [Graphics:Images/LaplaceTransformConvolutionMod_gr_78.gif].

Solution 4.


Converted by Mathematica      January 28, 2003