Can Jordan's Lemma be applied to clockwise contours?

In summary, the conversation discusses the use of Jordan's Lemma and its applicability to clockwise contours. The Lemma states that when the integration path is reversed, the sign of the integral is also reversed. However, since the conclusion of Jordan's lemma is that the integral goes to 0, reversing the integration path would not affect the result. Therefore, it can be used for clockwise contours as well.
  • #1
WWCY
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Homework Statement



Screen Shot 2017-10-23 at 7.33.47 PM.png


My notes state the Lemma as shown above. I believe one of the underlying conditions is that the arc we integrate over must be +ve oriented (anti-clockwise) in the Upper and Lower half of the Complex Plane. However my notes doesn't mention whether or not the result holds when we integrate over a -ve oriented arc.

My question is, does it hold for clockwise contours? If so (or not), why not?

Assistance is greatly appreciated!

2. Homework Equations

The Attempt at a Solution

 

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  • #2
When the integration path is reversed, the sign of the integral is reversed. Since the conclusion of Jordan's lemma is that the integral goes to 0, reversing the integration path just makes the integral go to -0 = 0.
 
  • #3
FactChecker said:
When the integration path is reversed, the sign of the integral is reversed. Since the conclusion of Jordan's lemma is that the integral goes to 0, reversing the integration path just makes the integral go to -0 = 0.

Is this to say that I can use Jordan's Lemma in a clockwise contour?

Thank you for your response.
 

What is Jordan's Lemma?

Jordan's Lemma is a mathematical tool used in complex analysis to evaluate integrals of the form ∫0f(x)eixdx. It states that if certain conditions are met, the integral can be approximated by a simpler function.

What are the conditions for Jordan's Lemma?

The conditions for Jordan's Lemma are:

  • The function f(x) must be continuous on the interval [0, ∞).
  • The integral ∫0|f(x)|dx must converge.
  • The function f(x) must approach 0 as x approaches infinity.
  • The integral ∫0sin(x)f(x)dx and ∫0cos(x)f(x)dx must both converge.

What is the purpose of Jordan's Lemma?

The purpose of Jordan's Lemma is to simplify the evaluation of complex integrals by approximating them with simpler integrals that are easier to solve. This can save time and effort in mathematical calculations.

Can Jordan's Lemma be applied to any integral?

No, Jordan's Lemma can only be applied to integrals of the form ∫0f(x)eixdx that satisfy the conditions listed above. If the conditions are not met, the approximation may not hold and the integral must be solved using other methods.

What are some practical applications of Jordan's Lemma?

Jordan's Lemma has various applications in physics, engineering, and other fields that involve complex mathematical calculations. It is commonly used in the analysis of electrical circuits, signal processing, and quantum mechanics, among others.

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