Square of Dirac delta function

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Discussion Overview

The discussion revolves around the mathematical properties of the square of the Dirac delta function, ##(\delta(x))^2##, and whether it retains the characteristics of a Dirac delta function or transforms into something else. Participants explore theoretical implications, definitions, and the behavior of the Dirac delta function in integrals.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant suggests that squaring the Dirac delta function still results in a Dirac delta function or a multiple of it, proposing that the area under the graph increases.
  • Another participant argues that squaring the Dirac delta function is fundamentally different from merely multiplying by a constant, referencing the rectangular approximation of the delta function and questioning the implications of squaring an infinite height.
  • A third participant clarifies that the Dirac delta function is defined by its integral behavior and emphasizes that it is a generalized function, not a traditional function, suggesting that the square of the delta function may not be defined in the same way.
  • A fourth participant provides a link to an external source that discusses the definition of the square of the delta function, indicating that there may be established discussions on this topic elsewhere.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the square of the Dirac delta function, with no consensus reached on whether it remains a Dirac delta function or transforms into something else. The discussion reflects multiple competing perspectives.

Contextual Notes

Participants highlight the distinction between generalized functions and traditional functions, and the implications of squaring a function defined in terms of its behavior under integration. There are unresolved questions regarding the mathematical treatment of such operations.

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Is the square of a Dirac delta function, ##(\delta(x))^2##, still a Dirac delta function, ##\delta(x)##?

A Dirac delta function peaks at one value of ##x##, say 0. If it is squared, it still peaks at the same value, so it seems like the squared Dirac delta function is still a Dirac delta function, ##\delta(x)##, or some multiple of it, ##k\delta(x)##, where ##k>1##, since the area under graph seems larger.

How about the square root of a Dirac delta function?
 
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It is something totally different than just multiplying by a constant.One thing to think about. The Del function is sometimes described as a rectangle of width d, and height (1/d) then take the limit as d->0. (so height approaches infinity)
At all values of d, you get an area of (d/d) = 1. But if you have (Del)^2, the width is essentially the same as Del, but the height is infinity^2 ?

WolframAlpha produced a surprising result for this. http://www.wolframalpha.com/input/?i=(DiracDelta[t])*(DiracDelta[t])
 
Last edited:
The Dirac delta "function" is defined by its behavior inside an integral: ∫f(x)δ(x)dx = f(0). It is a generalized function, not a function.
I think that your comment about an increased area of δ2 is confusing the delta function with an approximation of the δ function.
One approach to multiplying generalized functions is to separate them into their "smooth" and "singular" parts. In that, δ(x)2 = 0. (see https://en.wikipedia.org/wiki/Generalized_function#Algebras_of_generalized_functions)
 

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