Re{} and Im{} operators under the integral sign

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Discussion Overview

The discussion revolves around the conditions under which the real (Re{}) or imaginary (Im{}) operators can be interchanged with the integral sign in the context of complex functions. The scope includes mathematical reasoning and technical clarification regarding integrals involving complex variables.

Discussion Character

  • Technical explanation, Mathematical reasoning

Main Points Raised

  • One participant seeks clarification on the hypothesis required to swap the Re{} or Im{} operator with the integral sign.
  • Another participant questions whether the dummy variable in the integral is real or complex, suggesting it may affect the outcome.
  • A third participant explains that if the complex function is expressed as f(t) + g(t)i with t as a real variable, then the interchange is valid. They note that this leads to Re \int f(t)dt = \int f(t)dt + i\int g(t)dt.
  • However, they caution that this equivalence does not hold if f is a complex function of a complex variable.

Areas of Agreement / Disagreement

Participants express differing views on the conditions under which the operators can be interchanged, indicating that the discussion remains unresolved with multiple competing perspectives.

Contextual Notes

The discussion does not clarify the assumptions regarding the nature of the complex functions involved or the specific conditions under which the interchange is valid.

eliotsbowe
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Hello, I'm trying to figure out what hypothesis I need to swap the Re{} (or Im) operator and the integral sign, but I can't find anything on the matter. I guess either it's a trivial question or a rare one. Can someone help me?

Thanks in advance.
 
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is the dummy variable real or complex?
 
If your complex function is f(t)+ g(t)i where t is a real variable, and the integral is, say, [itex]\int Re(f)dt= \int f(t)dt[/itex], then, yes, that is the same as [itex]Re \int f(t)+ g(t)i dt[/itex] because that last integer is [itex]\int f(t)dt+ i\int g(t)dt[/itex].

If, however, f is a complex function of a complex variable that is not necessarily true.
 
thanks a lot!
 

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