Limit of u(t)- u(t -\delta) as delta goes to zero, LTI systems

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Discussion Overview

The discussion revolves around the limit of the expression yb(t) as delta approaches zero, specifically in the context of linear time-invariant (LTI) systems. Participants are exploring the implications of the unit step function and its derivative in relation to this limit.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Conceptual clarification

Main Points Raised

  • One participant presents the limit expression yb(t) and applies L'Hôpital's rule to part of it, arriving at exp[-t/RC]/RC, but expresses uncertainty about the behavior of u(t) - u(t - delta) as delta approaches zero.
  • Another participant suggests a related limit expression involving the unit step function, asking if it resonates with the original poster.
  • A third participant indicates a lack of familiarity with the unit step and Dirac delta functions, suggesting they are new to the topic.
  • A later reply clarifies that delta is merely a variable and proposes reframing the question in terms of the derivative of the unit step function, u'(t).

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the limit of u(t) - u(t - delta) as delta approaches zero, with some expressing uncertainty and others suggesting different perspectives on the interpretation of delta.

Contextual Notes

The discussion includes assumptions about the behavior of the unit step function and its derivative, which remain unresolved. The participants' varying levels of familiarity with the concepts may affect their interpretations.

Who May Find This Useful

Students or individuals interested in the mathematical properties of the unit step function and its applications in LTI systems may find this discussion relevant.

AMac33
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Homework Statement



what is the limit of yb(t) as \delta goes to zero.

yb(t) = (b/delta)*exp[-t/RC](exp[delta/RC] - 1)(u(t)-u(t-delta))

b=1.






2. The attempt at a solution

I used l'hospital's rule to find the limit of (b/delta)*exp[-t/RC](exp[delta/RC] - 1), which i got to be exp[-t/RC]/RC.

But I do not know what to do with the u(t)-u(t-delta). does it go to zero? or am I supposed to say it goes to delta(t)?

Any help/ advice would be appreciated, thanks!
 
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Does the expression

[tex]\lim_{\delta \to 0} \frac{u(t + \delta) - u(t)}{\delta}[/tex]
ring a bell?
 
honestly, no. I'm fairly new to the unit step and dirac delta function.
 
Oh, but this doesn't have to do with either of those. [itex]\delta[/itex] is just a variable, if it makes you feel any better you can call it x or (more commonly used) h

Maybe I should ask it the other way around: what is the definition of the derivative u'(t) of u(t) at t?
 

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