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Old 10-23-2002, 07:17 PM   #11
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That's not entirely true, Jesus. The Dirac Delta function, for example, has just the property you describe cannot exist (finite area with zero breadth). It's a fundamental part of much of basic physics theory, too (e.g. the charge density of a point charge, a very basic model for the surface periodic potential of solids in Quantum Mechanics, "unit basis vector operators" in certain vector spaces, and much more).
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Old 10-23-2002, 10:02 PM   #12
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Nice catch, Feather. But somewhat in defence of Jesus Christ (funny, I never thought I would say that), the "Dirac delta function" is technically not a function, but a "linear functional", a sort of generalised function. Here, this explains it better than I ever could:

<a href="http://mathworld.wolfram.com/DeltaFunction.html" target="_blank">Delta Function</a>

Although, I still don't fully understand it.
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Old 10-24-2002, 01:18 AM   #13
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A linear functional is a special case of a linear transformation, in which the codomain is the real numbers. In the case of the delta function, the domain is a set of functions, which is where the problem comes in. We are mapping a set of functions to the reals. I'm not sure that talking about zero breadth is meaningful in this context.

Its still a function. Its domain just doesn't happen to be a subset of the real numbers.
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Old 10-24-2002, 05:07 AM   #14
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Yeah, I knew that, Friar, but I figured it might irk some mathematicians to put it the way I did. You know, kinda like integrating F(x)dx from 0 to x.
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