Laplace / inverse laplace transform

Click For Summary

Discussion Overview

The discussion revolves around the application of the Laplace transform and its inverse in solving a differential equation, particularly focusing on the interpretation of terms involving delta functions and step functions in the context of the solution.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions why the inverse Laplace transform of $$\frac{-1}{s+1} + \frac{2}{s-3}$$ does not yield $$-e^{-t} + 2e^{3t}$$ for $$t>0$$.
  • Another participant suggests that the presence of delta functions on the right side of the equation alters the conditions under which the transforms are valid, implying that step functions are necessary for the solution.
  • A further inquiry is made regarding the specific values that determine the application of step functions and how they are utilized in the solution.
  • There is a question raised about the meanings of "\delta(x)" and "\delta'(x)", indicating a potential need for clarification on these concepts.

Areas of Agreement / Disagreement

Participants do not appear to reach consensus, as there are competing views regarding the role of delta functions and the conditions for the validity of the inverse Laplace transform.

Contextual Notes

The discussion highlights the dependence on the definitions of delta functions and the conditions under which step functions apply, which remain unresolved.

goohu
Messages
53
Reaction score
3
View attachment 9453

Problem: Find a (limited?) solution to the diff eq.

View attachment 9454
At the end of the solution, when you transform $$\frac{-1}{s+1} + \frac{2}{s-3}$$
why doesn't it become $$-e^{-t} + 2e^{3t} $$, t>0 ?
 

Attachments

  • prob.JPG
    prob.JPG
    6 KB · Views: 182
  • Sol.JPG
    Sol.JPG
    11.9 KB · Views: 173
Physics news on Phys.org
That would be correct if the right hand side of the equation were 0. But the delta functions on the right mean that those are correct only for x greater than certain values so the step functions are needed.
 
What values are those and how are the step functions used?
 
Do you know what "\delta(x)" and "\delta'(x)" mean?
 

Similar threads

  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 7 ·
Replies
7
Views
7K
  • · Replies 17 ·
Replies
17
Views
3K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 5 ·
Replies
5
Views
5K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 4 ·
Replies
4
Views
11K
  • · Replies 1 ·
Replies
1
Views
10K