Is the Integrator Linear in t?

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Discussion Overview

The discussion revolves around the linearity of a system, specifically whether an integrator is linear in the variable t. Participants explore the definitions and implications of linearity in the context of a homework problem, examining the conditions under which a function can be considered linear.

Discussion Character

  • Homework-related
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant asserts that they have shown the system is linear based on their understanding but questions why provided solutions indicate otherwise.
  • Another participant clarifies that linearity should be evaluated in terms of the variable t, specifically whether the condition x(a t1 + b t2) = a x(t1) + b x(t2) holds.
  • Some participants express confusion over whether the original problem is indeed linear, with one seeking confirmation about the linearity of their example problem.
  • There is a repeated emphasis on the distinction between linearity in x versus linearity in t, with participants questioning the clarity of the problem statement.
  • One participant mentions that they believe an integrator is linear and seeks to understand if their proof supports linearity in t.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the original problem is linear. There is a clear disagreement on the interpretation of linearity in the context of the problem, with some asserting it is linear while others challenge that interpretation.

Contextual Notes

Participants express uncertainty regarding the definitions and conditions necessary for establishing linearity, particularly in relation to the variable t versus the variable x. The discussion highlights potential ambiguities in the problem statement and the examples provided.

SuperCat
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Homework Statement


Determine whether the system is linear
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Homework Equations


Superposition

The Attempt at a Solution


I am comfortable solving the case where the bounds are from negative infinity to t. I have provided an example of that solution I found online. I attempt to solve that problem in a similar fashion and conclude the system is linear, but according to the solutions (no work just answers) I was provided with the system is not linear.
I would appreciate if someone could tell me where I went wrong (why the same procedure can't be applied) or whether I am correct.
6e3dd2fb7c3f230c6421ac8f5331b36b.png
 
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When you are asked whether a function x(t) is linear, the question is whether it is linear in t. In other words, is it true that x(a t1 + b t2) = a x(t1) + b x(t2)? You have shown that your function y(t) is linear in x, which it clearly is, but I doubt that is the question that was being asked. Perhaps the question should have been more explicit.
 
phyzguy said:
When you are asked whether a function x(t) is linear, the question is whether it is linear in t. In other words, is it true that x(a t1 + b t2) = a x(t1) + b x(t2)? You have shown that your function y(t) is linear in x, which it clearly is, but I doubt that is the question that was being asked. Perhaps the question should have been more explicit.
Thank you for your reply. I understand what you are saying. Most of the sample problems in my textbook demonstrate linearity by saying y(t) is linear in x.

Just to clarify, are you saying that the problem I posted is in-fact linear?
 
SuperCat said:
Just to clarify, are you saying that the problem I posted is in-fact linear?

No. To repeat, when you are asked whether a function x(t) is linear, the question is whether it is linear in t. In other words, is it true that x(a t1 + b t2) = a x(t1) + b x(t2)?
 
phyzguy said:
No. To repeat, when you are asked whether a function x(t) is linear, the question is whether it is linear in t. In other words, is it true that x(a t1 + b t2) = a x(t1) + b x(t2)?
Would that also suggest that the example problem I provided in 3 is non-linear?
 
SuperCat said:
Would that also suggest that the example problem I provided in 3 is non-linear?
Sorry, I don't understand your question. What exactly are you asking?
 
phyzguy said:
Sorry, I don't understand your question. What exactly are you asking?

The last image I posted where it says testing for linearity, that is testing just an integrator for linearity. I am aware that an integrator is linear. I want to know if that proof demonstrates it is linear in t.
 

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