Derivative of a special function

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    Derivative Function
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Discussion Overview

The discussion centers around the derivative of a special function defined with infinite values and discontinuities, specifically at the points x=0 and x=a. Participants explore the implications of the function's behavior and the concept of derivatives in the context of generalized functions.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents a function f(x) that takes infinite values outside the interval [0, a] and is zero within it, questioning the derivative at the boundaries.
  • Another participant suggests that the derivative of a jump of size a at a point u is represented as aδ(x-u), noting that in this case, a is -∞ and u is 0.
  • Some participants express that the function described may not qualify as a proper function, indicating that generalized functions are necessary for analysis.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the nature of the function or its derivative. There are competing views on the applicability of generalized functions and the interpretation of the derivative at the specified points.

Contextual Notes

There are limitations regarding the definitions of functions and derivatives being discussed, particularly concerning the use of generalized functions and the implications of infinite jumps.

orienst
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Let f(x) be the following function:

f(x)=\infty,if x<0 or x>a;f(x)=0,if 0<x<a.

What’s the derivative of f(x) at x=0 and x=a? I know that the derivative of step function is \delta(x) , but what will occur if the jump is infinite?
 
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f ' (x) = dx*f(x)
 
In general the derivative of a jump of size a at u is aδ(x-u). your a is -∞ and u=0.
 
JJacquelin said:
f ' (x) = dx*f(x)


mathman said:
In general the derivative of a jump of size a at u is aδ(x-u). your a is -∞ and u=0.

Thanks for your reply.
 
Note that the "function" you give is not really a function. And Jjaquelin and mathman had to use "generalized functions" to give an answer.
 

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