Diracs delta equation - general interpretation

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Discussion Overview

The discussion revolves around the interpretation of the Dirac delta function in the context of differential equations, particularly when it appears as a periodic external force in a spring system. Participants explore how to understand the implications of a Dirac delta function on the right-hand side of a differential equation and its periodic nature.

Discussion Character

  • Exploratory, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant seeks a general explanation of how to interpret a Dirac delta function in a differential equation, specifically questioning its periodicity and existence over time.
  • Another participant asserts that the function repeats itself, implying a periodic nature of the Dirac delta function.
  • A third participant introduces a mathematical construction involving a sequence of functions that converge to a periodic "delta function," suggesting that this represents a delta function at every multiple of 2π.

Areas of Agreement / Disagreement

There is no clear consensus on the interpretation of the Dirac delta function's periodicity, as participants present differing views on its behavior and implications.

Contextual Notes

The discussion includes assumptions about the nature of the Dirac delta function and its application in differential equations, which may not be universally agreed upon. The mathematical steps leading to the periodic interpretation remain unresolved.

finitefemmet
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Im really just searching for a general explanation!

If you are solving a pretty standard left hand side differential equation, but a diracs delta function on the right hand side. I am abit confused about how to interpret this.

If this is the case for the right hand side:

r(t) = Diracs (t) ,for 0≤ t<T with the period T=2∏

Think of this as an periodic outside force on a spring system, now I don't know how to interpret this. Does this mean that r(t) repeats itself, at t=0, t=2∏ and so on. Or that the diracs delta equation only excists between 0 and 2∏?

Since its a diracs delta equation, it cannot work over a longer time interval? Since its an instant impuls over an extremely small time space.

If anyone could shed some light over this, I would be most gratefull.
I am not looking for a solution, just general information on how to interpret this information with the diracs delta function

Thank you:smile:, and excuse my poor english!
 
Last edited:
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They mean that the function repeats itself
 
For every positive integer k, let fk(t)=
0 for 2(n-1)pi+ 1/k to 2npi- 1/k,
k/2 for 2npi- 1/k to 2npi+ 1/k

for n any positive integer. The periodic "delta function" is the limit of fk(x) as k goes to infinity. Essentially, that gives a "delta function" at every multiple of 2pi.
 
Thank you both;)
 

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