Is exp(i.x) with x=-infinity equal to zero?

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Discussion Overview

The discussion revolves around the evaluation of the expression exp(i.x) as x approaches negative infinity. Participants explore whether this expression converges to a specific value, particularly questioning if it equals zero, and delve into the implications of complex numbers and limits in this context.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • One participant questions if exp(i.x) with x = -infinity equals zero and notes that the decomposition into cosine and sine suggests non-convergence.
  • Another participant argues that the expression does not converge because it represents a complex number with a modulus of one, indicating that the argument cannot approach infinity without losing phase information.
  • A different participant states that the expression is undefined and questions the rationale for defining it at infinity.
  • One participant reiterates that the function is not defined at infinity, suggesting that there is no issue with the expression in this context.
  • A comment emphasizes the distinction between the concepts of convergence and numerical values, asserting that it is important to differentiate between limits and numbers.

Areas of Agreement / Disagreement

Participants express disagreement regarding the convergence of the expression, with some asserting it is undefined while others discuss the implications of the modulus and phase. No consensus is reached on whether the expression can be assigned a value as x approaches negative infinity.

Contextual Notes

The discussion highlights limitations in defining the behavior of complex functions at infinity and the nuances of convergence versus numerical values, without resolving these complexities.

sam2
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Hi all,

Looking for some help on the following problem. Any replies much appreciated.

I have the complex number

exp(i.x)

If x = - infinity,

is this zero?? Is there any intuitive/straightforward value that it should be? I decomposed the expression into cos and sin and it looks like the number doesn't converge to anything!

regards,
 
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Of course it doesn't converge.U need a complex number of different modulus.The one u've chosen has modulus one,i.e. 1.U cannot make it's argument go to infinity,coz that would mean rotating the unit vector (which is represented by e^(ix)) an ininite amount of times and the phase could not be determined.

Daniel.
 
It is undefined, and there is no reason why it should be defined.
 
sam2 said:
Hi all,

Looking for some help on the following problem. Any replies much appreciated.

I have the complex number

exp(i.x)

If x = - infinity,

is this zero?? Is there any intuitive/straightforward value that it should be? I decomposed the expression into cos and sin and it looks like the number doesn't converge to anything!

regards,

Well, it doesn't go to infinity because of the very reason that you quoted. But don't worry : there is NO problem because this function is NOT DEFINED in the infinity. So, there is no problem and why should there be any ?


marlon
 
Got it.

Many thanks for the replies.

Regards,
Sam
 
A comment: a number is a number, it doesn't make sense to say it "converges" to anything. While the distinction is often blurred, it is still important to remember that the concept of limit is different than that of a number.
 
Last edited:

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